Th Ti and Plac of Frtilization of th Goldn astr Egg by FRITZ STRAUSS Fro th Dpartnts of Anatoy, Univrsity of Wisconsin, Madison, Wisconsin, and Univrsity of Brn, Switzrland INTRODUCTION TERE is littl prcis inforation in th litratur as to th xact plac whr th union of th al and fal gats occurs in th gnital tract of aals. Yt it ss that an xact knowldg of th plac of frtilization ight b of grat significanc, not only for our undrstanding of th procss of frtilization itslf, but in its rlation to th anifold probls associatd with th liitd span of ti during which th capacity for frtilization prsists in th spr and gg, and to th physiology of latr dvlopnt and iplantation. In ost writings about th arly dvlopnt of Man and othr aals, it is assud that th gg is frtilizd in th cphalic part of th oviduct. owvr, thr is still insufficint vidnc to justify such gnral assuptions. It would not b surprising if it should b shown that diffrnt spcis hav diffrnt topographical positions of th frtilization sit corrlatd for instanc with such factors as spontanous vrsus inducd ovulation. Such an unsatisfactory situation suggsts th ncssity of a rviw of our knowldg concrning th sit of frtilization of th aalian gg, and otivatd to invstigat this probl. MATERIAL AND METODS This first study is basd on th xaination of 8 frtilizd and unfrtilizd ggs fro goldn hastrs, Msocrictus auratus Watrhous. Th hastr was chosn bcaus of its xact adhrnc to an asily dtrind sxual cycl. It ovulats spontanously vry days in th arly orning hours btwn and o'clock of th scond day of th strous cycl (Ward, 9; Boyr, 9). Th ar dischargd at any stag fro 'first anaphas' to 'first polar body, scond taphas' (Ward, 98a). Th anials usd in this invstigation wr slctd on th basis of sipl daily vaginal inspction using th data of Ward (9). This thod has provd to b without failur. Author's addrss: Dpartnt of Anatoy, Univrsity of Brn, Buhlstrass, Brn, Switzrland. [J. Ebryol. xp. Morph. Vol., Part, pp. -, March 9]
FERTILIZATION IN TE AMSTER Instad of th copulation and ovulation ag of ost authors (Gravs, 9; Vnabl, 9; Boyr, 9), I startd y xprints using th dvlopntal ag of th frtilizd as dfind by Ward (98ft) but subsquntly changd to a or ralistic ti scal, basd on a rvisd stiat of ovulation ti, as a rsult of obsrvations to b givn latr. Dvlopntal ag is th ti span fro th arlist possibl frtilization ti of an gg until its irsion in fixativ. Th dvlopntal ags includd in y sris wr,,,,,, 8,, and hours according to Ward's data on ovulation ti. For ach ag half of th anials had short priods for copulation in th vning (8.-8. p..) bfor ovulation. Th othr half had a half-hour priod for copulation in th orning about a.. aftr ovulation. Sinc Ward assus th ti of ovulation is a.., th dvlopntal ag and ovulation ag would corrspond in anials atd in th vning; in th anials atd in th orning th dvlopntal ag would b hours lss than th ovulation ag. Unatd anials killd at th sa ti as ths xprintal sris ford controls. Th ntir gnital organs wr fixd idiatly aftr dath in Bouin's fluid. Th ris with th oviducts and conncting parts wr bddd in paraffin fro cyclohxanon, sctiond at 8 /JL, and staind with iron hatoxylin (Wigrt) without countrstain. Th tortuous pattrn of th utrin tubs of th goldn hastr ad it xtraordinarily difficult to stablish th xact position of th tubal ggs. Thrfor it was ncssary to draw th whol oviduct sction by sction aftr cutting, rcording th rlativ position of th fal gats or zygots. At th sa ti histological diffrncs in th construction of th wall of various lvls of th oviduct wr notd. OBSERVATIONS Th hastr ry is, as in any rodnts, copltly nclosd by an rial sac which is continuous with th infundibulu of th oviduct (Txt-fig. ). Th lngth of th infundibulu is about. Th transition fro th sooth bursa wall to th funnl is charactrizd by th apparanc of rlativly high and slndr ucous folds or fibria which contain only a vry dlicat connctiv tissu frawork. Th infundibulu lads into th apulla, which is about. long. Its wall is thin, rlativly non-uscular, and contains low, widbasd ucosal ridgs at rathr rgular intrvals. Toward th isthus th apulla wall gradually incrass in thicknss, so that a sharp boundary btwn ths two portions dos not xist. It provd usful to dsignat a transitional sction, about. in lngth, btwn th apulla and isthus. Th isthus (approxiatly -. long) has a arkdly narrowr lun than th prcding sction of th oviduct, and carris nurous thick pithlial ridgs which whn cut prpndicularly appar sowhat club-shapd. In th transition fro th isthus to th utrin horn th nubr of ridgs dcrass, and thy bco
F. STRAUSSTIME AND PLACE OF FERTILIZATION lowr. Th lun hr bcos indntd by sall sparat protrusions. In th tunica propria glands appar; ths incras in nubr and dinsion and ark transitional ri TEXT-FIG.. Schatic drawing of th oviduct and ry in Msocrictus auratus Watrhous. Th various sgnts of th oviduct ar diffrntiatd by th diffrnt contours of th lun. th bginning of th utrus. In addition, a valv occurs at th tubal-utrin junction. In brif th oviduct of th hastr corrsponds in structur and histology with that of th ous as givn by Sobotta (89).
TABLE Distribution and condition of th ggs fro th atd anials according to hypothtical ovulation ag (ovulation assud at a..) and ti of ating Mating = orning = vning.. Estiatd ovulation ag in hours 8 8 8 anials corpora luta 9 8 Total no. of 8 Matur within th ry ovulatd 8 non-frtilizd frtilizd 9 9 9 9 issing Xw CO W9
F. STRAUSSTIME AND PLACE OF FERTILIZATION In Tabls (xprintals, atd) and (controls, unatd) th distribution of 8 ggs in rlation to thir assud ovulation ag is prsntd. Th ggs classd as 'issing' includ both thos for which a saf valuation of thir condition was not possibl, and ggs which could not b found but which ust hav xistd sinc thr wr or rupturd follicls or corpora luta than rcovrd ggs. TABLE Distribution of th in th control (unatd) anials, groupd according to ovulation ag to corrspond with th xprintal (atd) anials Estiatd ovulation ag 8 8 8 anials corpora luta Total no. of Matur within th ry tubal 9 8 9 issing to to to to to to to to to to to to Tabls and prit an stiat of th nubr of which ust hav bn producd fro polyovular follicls. For th total nubr of 8 ggs thr wr 9 corpora luta and rip follicls, so that thr wr or ggs than follicls, ithr unrupturd or lutinizd. In othr words 9 pr cnt, of th s to hav bn drivd fro polyovular follicls. Th planning of th xprint was basd on th assuption that ovulation occurs in th Syrian hastr at approxiatly a.. (Ward, 9, 98ft). In y obsrvations, howvr, at a.. rip ggs out of 9 atur (Tabls and ) had not yt lft thir follicls. A fw rip follicls ay prsist, or dgnrat through lutinization or atrsia; thir nubr is sall copard to th nubr of xplld ggs. W also know that in an anial such as Msocrictus whr a grat nubr of ggs ar xplld w should not xpct all rip follicls to ruptur, as a sall prcntag ay bco atrtic vry lat in dvlopnt, just bfor ruptur. Ovulation taks plac at a sowhat latr ti than that givn by Ward. r statnt is basd on 8 ris of 8 anials killd btwn idnight and. a.. Only on of rip follicls had rupturd at idnight. In th short tiintrval fro. to. a.. Ward (9) found thr rupturd follicls, on
TABLE Ag and distribution of ggs in th various sgnts of th oviduct in th atd anials. Th nubrs in parnthss ar th nubrs of frtilizd ggs. In colun on, and an orning and vning ating rspctivly Estiatd ovulation ag O 8 8 8 Total no. of Matur within th ry tubal Pririal sac in th various sgnts of th oviduct: Infundibulu () Uppr () Apulla Middl () () () () () Lowr () () () () 8 (8) () KD Transitional sction () () 9(9) () KD () KD () () Isthus id) () 9(9) (8) () 9 () 8(8) (9) () () XW
Estiatd ovulation ag 8 8 8 TABLE Ag and distribution of ggs in th various sgnts of th oviduct in th unatd controls, groupd according to ovulation ag to corrspond with th xprintal (atd) anials Total no. of 9 8 9 Matur within th ry z z tubal 9 8 9 Pririal sac z z Infundibulu in th various sgnts of th oviduct: Apulla Uppr Middl Lowr z 9 z Transitional sction z Isthus 9 8 9 CO C CO CO >! O > ow w II r ii N O
IN TE AMSTER 9 in th procss of rupturing, and 9 unrupturd follicls. alf an hour latr (. and. a..) follicls had rupturd, follicls wr just rupturing, and 9 wr unrupturd. In y fals killd at a.. only out of 9 rip follicls had rupturd. According to Ward's findings (8 follicls) and y data (9 follicls) only out of 9 atur follicls had rupturd btwn idnight and a.. At and a.. thr wr no or follicls rady for rupturing. All th Graafian follicls at that ti showd arly signs of atrsia. So it ss doubtful whthr th high point of ovulation actually lis at a..: it ss rathr to b an hour or two latr. It appars on a basis of 9 rip or frshly rupturd follicls that th pak of follicular ruptur occurs btwn and a.., i.. on th avrag at - a.. This corrsponds to th ovulation ti of th ous (Snll, 9). All th following ti data ar basd on an assud ovulation ti of a.. Th ain data of th rsults ar givn in Tabls -. A fw inor points, howvr, which cannot b obtaind fro th tabls, ar dalt with in th txt. At a.. of ovulatd ggs (cobining th atd and unatd groups) wr found in th bginning part of th apulla (Tabls and ), and only thr lay in th pririal spac. Two hours aftr th assud ti of ovulation, of 8 ggs wr found in th apulla (Tabls and ), whil ggs still raind in th infundibulu. On of ths in which th had of a spr was visibl was in th taphas of th scond aturation division. Sinc ggs wr not found in th infundibulu at a latr ti, it is concludd that th quickly pass th pririal spac and th infundibulu. Approxiatly hours aftr ovulation all ggs should hav rachd th apulla through which thy slowly pass during th nxt - hours. Th schatic diagra (Txt-fig. ) shows, along with th tortuous natur of th tub, th ggs on thir journy through th oviduct, whr in th cas of a ating thy ar frtilizd. Tabl shows that th first frtilizd ggs ar found hours aftr th supposd a.. ovulation; spr had thn pntratd into of ovulatd. Thr of ths zygots lay in th iddl part of th apullar rgion, whil on gg was alrady frtilizd in th cranial portion and anothr in th infundibulu. On,, and hours aftr stiatd ovulation ti unfrtilizd and frtilizd ggs wr in th apulla copard to only in th infundibulu. By hours ovulation ag th nubr of unfrtilizd diinishs rapidly. Thrfor w can assu that frtilization in th infundibulu is th xcption rathr than th rul. Eight hours aftr stiatd ovulation ti of ggs wr frtilizd, or just in th procss of frtilization; th spratozoa had partially pircd th brana pllucida in so, whil in othrs thy wr in th act of pntrating into th gat, or had just pntratd. Th zygots lay in th slightly dilatd id- and caudal rgion of th apulla (Tabls and ). So of th ggs with an stiatd ovulation ag of hours (Tabls and ) wr in th procss of frtilization. Th had of th spr was partly transford into th al pronuclus. Th haploid gg nucli wr in th anaphas 8. v
TABLE Distribution of th arly dvlopntal stags of th goldn hastr according to ovulation ag. In colun on, and an orning and vning ating rspctivly O 8 8 8 Estiatd ovulation ag tubal to to UI UI Unfrtilizd Frtilizd 9 9 9 9 Spr prsnt Frtilization: Scond iosis z Pronucli z z 9 8 9 9 8 st clavag 8 -cll stag 9 -cll stag tol = GO c co coi w > ow w ii r h N ii O
TABLE Distribution of zygots in rlation to th diffrnt parts of th oviduct dvlopntal stags in th various sgnts of th oviduct Pririal sac Infundibulu.... Apulla: U p p r.... Middl.... Lowr.... Transitional sction. Isthus..... tubal 8 8 Unfrtilizd 9 Frtilizd 9 Frtilization: Spr prsnt 8 Scond iosis Pronucli 8 8 st clavag 9 9 -cll stag 9 -cll stag
F. STRAUSSTIME AND PLACE OF FERTILIZATION or tlophas of th scond iosis. If th ating occurrd or vn hours aftr th prsud ovulation ti thn out of frtilizd ggs with an ovulation ag of - hours had rachd th pronuclus stag; in only on gg had th spr pntratd shortly bfor dath (Tabl ). This gg, orovr, was th only on of this xtnsiv atrial that was still in th bginning phas of frtilization hours aftr th stiatd ti of ovulation, and hours aftr copulation. With an stiatd ovulation ag of about hours, copulation having prcdd ovulation by about 8 hours, of zygots in th transitional rgion still possssd both pronucli, in othrs th first clavag had occurrd, and wr in th two-cll stag. Th 9 ggs lying in th isthus wr in th pronuclus stag (Tabls and ). Only on bryo with an stiatd ovulation ag of hours, copulation having occurrd about hours aftr ovulation as a rsult of a orning ating, lay in th transitional rgion in th two-cll stag; th raining ggs had rachd th isthus. Twnty-two hours following th stiatd ti of ovulation, in anials atd th vning bfor, of bryos in th isthus had alrady dvlopd to th two-cll stag, whil in th transitional rgion and in th isthus showd pronucli; in on th nucli wr in synapsis. With an ovulation ag of 8- hours, aftr a orning copulation, in of th zygots in th transitional ara th first clavag was occurring whil on bryo was at th two-cll stag. In th isthus 9 ggs wr in th pronuclus stag, 9 in th first clavag stag, and two-cll stags, whil ggs wr still in th scond aturation division (Tabl ). With an assud ovulation ag of - hours, copulation having followd about hours aftr ovulation (Tabl ), zygots in th transitional rgion wr at th first clavag stag. Of th 8 frtilizd ggs lying in th isthus only zygots wr in th pronuclus stag. In on gg thr was first clavag, and bryos wr in th two-cll stag; on stragglr still in th scond iosis lay in th lowr apulla (Tabl ). DISCUSSION It is hardly probabl that in vry cas all ggs ovulatd ( pr anial) will b frtilizd. According to th data it appars that in at ost of 8 anials all ovulatd ggs wr frtilizd (Tabl ). Twlv or or hours following ovulation 9 pr cnt, of th ggs ovulatd wr frtilizd, and this ay b xpctd to approxiat th axiu for th goldn hastr, about 9 pr cnt, of th ggs shd raining unfrtilizd. Aong, hours following th stiatd ti of ovulation and hours aftr copulation, th bginning of frtilization was obsrvd in only on cas. Fro this I conclud that at an incrasd ovulation ag no furthr frtilization occurs, dspit th prsnc of spr.
IN TE AMSTER Th arlist frtilization of th hastr gg in vivo thrfor occurs at an ovulation ag of hours, whil th ability to b frtilizd dcrass rapidly at about hours aftr follicular ruptur. Th optiu ti for frtilization for th hastr gg is thrfor liitd within th rang fro to hours aftr ovulation. During this intrval th gg stays in th apulla. It appars that no othr plac than th apulla can rasonably b considrd as a frtilization sit; rcntly frtilizd ggs in variabl nubrs wr found in th iddl as wll as in th lowr rgion of th apulla. Th ggs obviously passd through th cranial portion of th apulla in a short ti. Thus at a.. 9 ggs lay in th bginning portion of th apulla, whil had alrady appard in th id-apullar rgion. Two hours latr 9 ggsaong th on frtilizdwr found in th cranial third of th apulla, and in th iddl third. Two hours latr still, that is at an stiatd ovulation ag of hours, no ggs wr found in th cranial apullar sgnt. Alost all of th ggs lay in th slightly dilatd iddl third, whil a fw had rachd th caudal sction. Fro this it is clar that until th pak of frtilization ti is rachd, btwn and hours aftr ovulation, th gg will b found in th id- and caudal third of th apulla. Thr thy s to b in th ost favourabl position for frtilization, for only on arly frtilization stag lis in th cranial third of th apulla (Tabl ). It ay b concludd thrfor that th union of th gg and spr in th goldn hastr taks plac as a rul in th iddl and lowr third of th apulla. Nvrthlss, frtilization can occasionally occur in th cranial nd of th apulla as wll as in th infundibulu. According to y obsrvations that frtilization of th goldn hastr gg occurs chifly in th iddl and caudal third of th apulla, th probl rains as to how far th orning ating ( hours aftr ovulation) possibly influncs th position of th frtilization sit. At th ti of th orning copulation ( a..) practically all ggs xplld hours bfor had rachd th iddl and caudal portion of th apulla. Thy stayd thr until thy rachd an avrag ovulation ag of hours. Sinc th spratozoa nd a iniu ti of hours to travl up to th apulla, thy would t ovulatd about 8 hours prviously. Th travlling ti of th sprs to th rgion of frtilization follows fro th fact that th first frtilizd ggs aftr a orning ating wr found in th apulla at th arlist hours post coitu. Th apullar ggs of fals killd bfor this ti ar still unfrtilizd (Tabls and ). If ating took plac in th vning bfor follicular ruptur, th first spratozoa ar alrady in th apulla at th ti of ovulation. Thrfor it is surprising not to find all th frtilizd in th apulla hours aftr ovulation. At this ti and in spit of th prsnc of sprs only out of ggs wr frtilizd (Tabl ). A short ti latr th proportion of zygots incrass rapidly. This finding supports th ida that th frshly ovulatd hastr gg is incapabl of bing frtilizd. Th ovu nds to ag in ordr to attain th capacity for frtilization. Tabl indicats clarly that hours aftr ating and at an ovulation ag of 8
F. STRAUSSTIME AND PLACE OF FERTILIZATION hours, on of ggs lying in th id-apullar rgion was frtilizd, and of of th caudal third. In th cours of th two following hours ( aftr copulation, aftr stiatd ti of ovulation) vn or gats will b frtilizd, whras th ggs that arrivd arlir wandr furthr. Thus I bliv that th orning ating dos not caus a shift of th frtilization sit. On th othr hand, ggs of an ovulation ag of or or hours ting th spr whn th ar alrady laving th frtilization sit, show a rapidly dcrasing frtilization capacity. It bcos zro whn th ating occurs 8 or or hours aftr ovulation (Ward, 9). In th pronuclus stag th hastr zygot lavs th frtilization sit to appar in th transitional sction. W find th first ggs thr hours aftr th hypothtical ti of follicular ruptur. Th last of th rach that part of th oviduct at an ovulation ag of hours. In th anti, howvr, th first - hour zygots hav alrady ntrd th isthus. Thus, practically all th ggs hav lft th apulla by -8 hours aftr ovulation and ar found ithr in th transitional sction, or hav alrady ntrd th isthus. Thrfor it ay b concludd that hours aftr follicular ruptur th gratr portion of th fal gats and zygots had lft th transitional sction. Th prsnc of spratozoa in th apulla and frtilization do not influnc th igration tpo in th apulla, for in th control anials th arrival of th within th transitional sction occurs btwn and hours aftr ovulation. Thrfor, it is justifiabl to assu that th ggs ov rlativly rapidly, within a axiu of hours, through th transitional sction. Fro coparison of Tabls and on rcivs th iprssion that th ggs ay rain in th transitional sction longr in th atd anials than in th controls. In th atd anials 9 pr cnt, of th ggs wr found in th transitional sction against 9 pr cnt, in th control anials. Th diffrnc btwn ths valus lis possibly outsid th argin of rror. Furthror, on ust not ovrlook th fact that to hours aftr follicular ruptur ( pr cnt.) of ggs wr dtaind in th transitional sction; of ths wr frtilizd. In this sa ti intrval in th atd anials, ggs (aong th zygots) had rachd th isthus. In th control sris, howvr, thr wr no stragglrs; all had rachd th isthus by hours. This apparnt contradiction is supportd by th fact that a sallr proportion of th ggs ( pr cnt.) travl rathr or slowly through th transitional sction than do th principal ass and th unfrtilizd ggs. Thr ar no data to xplain this. It is concivabl that ths rtardd ggs xprinc a variation siilar to th rtardd frtilizd rat and guina-pig gg as dscribd by Blandau & Jordan (9) and Blandau & Young (99). Sinc vry fw xact invstigations xist on th frtilization sit of th aalian gg, it is difficult to copar ths rsults with othrs and to classify th critically. Th findings of Sobotta, howvr, vrifid by Krr (9), wr of grat valu in this work. Th sction of th tub known as th frtilization sit of
IN TE AMSTER Sobotta conncts with th apulla and shows any apullar charactrs. Consquntly on is justifid in stating that frtilization in th hastr and th whit ous taks plac in ssntially idntical sctions of th apulla. In dscribing frtilization of th rat gg Tafani (889), Sobotta & Burckhard (9), and ubr (9) adhr closly to th prsntation givn by Sobotta for th ous. Thy obsrvd th frtilization sit in th rat as a widnd vsicular sction of th apulla which copars to th iddl third of th apulla in th goldn hastr. According to Rin (88), Rubaschkin (9), and Las (9) a siilar rlationship ss to xist in th guina-pig. Evn though thir data ar not as xact as would b dsirabl for coparison, it ss that th union of th two gats in Cavia likwis occurs in th apulla. Whn aond (9) spok of th proxial nd of th oviduct as th frtilization sit for th rabbit gg th apulla was ant. Fro th data givn by R. van dr Stricht (9), and by ill & Trib (9), th frtilization in th cat occurs in th proxial third of th tub and th apulla should likwis b undrstood. Th tptation is grat to tak th rsults basd on th invstigation of thr rprsntativs of th faily Murida, and to assu whn th frtilization sit is said to b in th apulla that it is always th sa sction of th apulla. On should b cautious about such gnralizations until nw invstigations hav brought to light furthr dtails of this qustion. On th basis of prsnt findings it cannot b said that all aalian ggs ar frtilizd in th sa ara (Strauss, 98,9). In th sa way nithr a faily-spcific nor vn an ordr-spcific frtilization plac can b stablishd at th prsnt ti. SUMMARY. Th iddl and caudal third of th apulla tuba ar th rgions whr ost of th ggs of Msocrictus auratus Watrhous ar frtilizd.. Th arlist frtilization rsulting fro vning atings prior to ovulation (assuing th ovulation pak to b at a..) wr obtaind at hours aftr ovulation. Whn copulation occurrd th orning aftr ovulation, frtilizd wr not obtaind at hours aftr ating, but thy wr at hours.. Th ti of frtilization is ost frquntly btwn th nd and th hour aftr ovulation. About 9 pr cnt, of th ggs ar frtilizd during this priod.. On th basis of xisting data it is not possibl to spak of a faily-spcific or vn an ordr-spcific frtilization sit for th aalian gg. ACKNOWLEDGEMENTS This invstigation was aidd by th Wisconsin Aluni Rsarch Foundation and by grants fro th Arican-Swiss Foundation for Scintific Exchang, Inc., and th Swiss Acady of Mdical Scincs. Th author wishs to xprss his profound gratitud to Dr.. W. Mossan
F. STRAUSSTIME AND PLACE OF FERTILIZATION for his invitation and aid in this study, which was ostly carrid out in his laboratory. Furthror, th author is indbtd to Dr. Margart W. Orsini for so advic, hlp in th xprints, and for us of crtain data. REFERENCES BLANDAU, R. J., & JORDAN, E. S. (9). Th ffct of dlayd frtilization on th dvlopnt of th rat ovu. Ar. J. Anat. 8, -9. & YOUNG, W. C. (99). Th ffcts of dlayd frtilization on th dvlopnt of th guinapig ovu. Ar. J. Anat., -9. BOYER, C. C. (9). Chronology of dvlopnt for th goldn hastr. /. Morph. 9, -8. GRAVES, A. P. (9). Dvlopnt of th goldn hastr, Crictus auratus Watrhous, during th first nin days. Ar. J. Anat., 9-. AMMOND, J. (9). Th frtilisation of rabbit in rlation to ti. /. xp. Biol., -. ILL, J. P., & TRIBE, M. (9). Th arly dvlopnt of th cat (Flis dostica). Quart. J. icr. Sci. 8, -. UBER, G. C. (9). Th dvlopnt of th albino rat, Mus norvgicus albinus. J. Morph., -8. KREMER, J. (9). Das Vrhaltn dr Vorkrn i bfruchttn Ei dr Ratt und dr Maus it bsondrr Brucksichtigung ihrr Nucloln. Z. ikr.-anat. Forsch., -9. LAMS,. (9). fitud d Fouf d cobay aux prirs stads d l'bryogns. Archivs d Biologi, Lig & Paris, 8, 9-. REIN, G. (88). Bitrag zur Knntnis dr Rifungsrschinungn und Bfruchtungsvorgang a Saugtiri. Arch. ikr. Anat., -. RUBASCKIN, W. (9). t)br di Rifungs- und Bfruchtungsprozss ds Mrschwinchnis. Anat. ft, Arb. anat. Inst., Wisbadn, 9, 9-. SNELL, G. D. (9). Biology of th Laboratory Mous. Philadlphia: Th Blakiston Copany. SOBOTTA, J. (89). Di Bfruchtung und Furchung ds Eis dr Maus. Arch. ikr. Anat., -9. & BURCKARD, G. (9). Rifung und Bfruchtung ds Eis dr wifin Ratt. Anat. ft, Arb. anat. Inst., Wisbadn,, -9. STRAUSS, F. (98). Di Bfruchtung und dr Vorgang dr Ovulation bi Ericulus aus dr Faili dr Cnttidn. Bioorphosis,, 8-. (9). Das Probl ds Bfruchtungsorts ds Saugtiris. Bull, schwiz. Akad. d. Wiss., 9-8. VAN DER STRICT, R. (9). Vitllogns dans l'ovul d Chatt. Archivs d Biologi, Lig & Paris,, -8. TAFANI, A. (889). La f"condation t la sgntation tudi's dans ls cufs ds rats. Arch. ital. Biol,,-. VENABLE, J.. (9). Pr-iplantation stags in th goldn hastr (Crictus auratus). Anat. Rc. 9,-9. WARD, M. C. (9). A study of th strous cycl and th brding of th goldn hastr, Crictus auratus. Anat. Rc. 9, 9-. (98a). Th aturation divisions of th of th goldn hastr. Anat. Rc.,. (98). Th arly dvlopnt and iplantation of th goldn hastr, Crictus auratus^ and th associatd ndotrial changs. Ar. J. Anat. 8, -. (Manuscript rcivd 9:iv:)