474: REPORT OE;ji|jO]^i>g§§I:^^PpF yI^||M^l^^^^ [?0]; 



"5. Divi«iou of the vspindle iuto two lia^yeg, oue remaipiug in the egg, 

 the other in the prominence; the pr<m)inpBQ.%l]ftGpiniiig,att,t]ti8 s,aiBe,tjLn[iQ,. 

 nearly constricted off from the .egg.3S.,ar p,o]9;y;<6eJ^-KrT ibr/ ^.xiiT .rr lovo 



"C. The formation of a second polar cell in the same. inaflniei?i.asr>tli€?! 

 fii:§t5 part of the spiu<Ue still remaa,uin.g,, in, the egg. : .: . -: ,, ';:;i, ,■:;(, 



l^jf Z. Conversion of t^l^e ,parjb qf,.,|>Ji§;Sg^f idla r^mfiining in; the^ egg: intftv 

 a nucleus— the female pronucleus- : .,; if;:3ia(i<il .v > : >;-\:i v!;u'; u,:, 



" 8. Transportation of _ the ffegialgj prQ^AijQleus ^towarda rthe ,centeit of 

 thaegg.- •, , . ly;.-) miyUi.BxUiO baoh 



"9. Entrance of a single spermatozofMi into the egg. ; : ..: . 



*f 10. Conversion of the hea,^ of the .spermatqzooii iutQ, a ^jiuqleHSmtlier: 

 male pronucleus. ,-£; j ^[^uovmna :tfj)m (rm hhnn eo-it yd!T Jvsioioo ^biioi 



"H. Appearance of- radialrstrioB: rouijdiihe TOaleipi^QPlItiJ^usp^MejKi 

 gradually travels towards the; female pronucleus.; ; u bi;^ Ju.-d -uij -iH'iH 



"12. Fusion of male and female pronuclei to form the first segmenta- 

 tion nnclens.'' '•- --'' '"'-■■' ''■0;^.A.-:si-^.iri.i;ii — .<. 



The foregoing accountis esse^ti,ally the sequence;0f events asohsiqryed 

 by Fol in Asferlas glaciaJis. This series of events evidently does not 

 hold for all forms. Thus, in Hini(llnea,i\toUusca, and NemafoideaimjiTeg^^ 

 nation takes place normally helbre the extrusion of the ])olar bodies is 

 completed (Balfour), so that the event which stantls as ninth in the pre- ' 

 ceding scheme would actually stand first, as in the case of the egg of' ^ 

 0.sfrm, where no disposition's manifested to extrude polar gjobules 

 until the ova are brought into contact with the spermatozoa. In the 

 case of the lamprey, Kupffer and Beneche have slioNyn that only one 

 spermatozoon enters the egg, but that others jkiss through the vitelline 

 njenibrane, and are taken into a peculiar i)rot<)plasmic protuberance of 

 the ovum which appears after'impregnation. In ova of Ostrea virgmica 

 which have been killed and hardened in osniic! acid the pellucid tract 

 which penetrates the egg for some distance in the vichiity of the polar 

 globules probably represents the axis of the amphiaster formed at the 

 time of the development of those bodies. ^ [ 1 'a^nij, well assured of the 

 fiict that no tendency toward a reorganization, of the centrally placed 

 nucleus of the mature egg of the oyster is ever manifested until it is' 

 brought into contact with spermatozoa. The egg of tlie osseous fish, is ; 

 scarcely referrible to either of the foregoing categories ; it has lost the' 

 germinal vesicle as a central structure before it leaves the parent folli- 

 cle, and coincident with the development of t|ie germinal peliicle or 

 germinal protoplasm which covers the yelk or deutoplasm, its sufetance 

 has probably been mostly transferred to that layer." As we now know 

 tliat the germ disk is formed at the time of impregnation or independ- 

 ently of it, it is to be supposed that in this process the germjnative 

 vesicle or its remains may not impji;obably undergo a complex metamor- 

 phosis. Although I have not'yet met with anything that I could regai^d 

 as undoubted pol^r cells, a minute prominence occurs on the disk of 

 tne cod which may oe i*egardea as feucn, or as an apparatus for the 



