Tin: n:< . EM <>K ( i.i:.\ 71 



into equal and un qua!, and paitial into discoidal and tOpertoUl. A' 

 .same time II AKfK 1:1. endeavoured to derive t !.. iill'ci 1.1 nu-tliids <.f cleavage 

 1'rom one another, and apropos of this directed attention to t In- in,; 

 of the nutritive yolk. 



The prooeMM which take place within tin- yolk have eluded observation 

 and a correct intei -pretat i >n even in. ire than the external phenomena of < 

 age, so that it is only in the most recent time> tha- ed a satis- 



factory insight into tliiMii. It is true that tin- proMein, as to r the 



nucleus plays in segmentation, has had the uninterrupted attention of in, 



I, but without any solution having been found. Foi -re in 



the literature two opposing views: sometimes one of them, sometimes the 

 other, attained temp. .rarily greater currency. According to one view which 

 was almost universally adopted by the botanists, and was defended on the 

 :ical side principally by REICH KUT, and even recently by AUERBACH 

 the nucleus disappears before every division, and is di>sol\ed. to be afterv. 

 formed anew in each daughter-segment; according to the other view the 

 nucleus, on the contrary, is not dissolved, but is constricted, becomes 

 dumb-bell-shaped, and is divided into halves, and thereby induces cell-division. 

 This \iew was taught especially by such zoologists and anatomists as C. E. 

 v. BAER, JOH. MCLLEK, KOLLIKU:, I.KYDIG, GEGENBAUR, HM:I KI:I. v\\ 

 I IM:IH:N. and others, who were supported by the observations which they 

 had made on transparent eggs of the lower animals. 



Light was tir.st thrown on the dispute 1 question at the moment when suit- 

 able objects were studied with the aid of higher magnifications, and especially 

 with the employment of modern methods of preparation (fixing and staining 

 reagen 



a works of FOL, FLEMMINC. x HM;I 1.1:1:. and AUERBACH on the cleavage 

 of the eggs of various animals mark a no advance. They still main- 



tained, it is true, that the nucleus is dissolved at the time of cleavage, but they 

 gave a detailed and accurate description of the striking radiation which arises 

 in the yolk upon the disappearance of the nucleus, and which during the 

 constriction of the egg soon becomes visible in the region of the daughter- 

 nuclei.* SCHNEIDER observed parts of the spindle-stage. 



Soon after this a more exact insight into the complicated and peculiar 

 nuclear changes was obtained by means of three investigations, which were 

 arried out independently and simultaneously on different objects, and were 

 published in rapid succession by BttTSCHi.i, s n:.\sr,ri:<;i:i:, and the author. 

 It was definitely established by these observations that there is no dissolution 

 of the nucleus at the time of division, but a metamorphosis, such as has been 

 described in the preceding pages. At the same time I likewise, proved that the 

 egg-nucleus is not a new format inn. but is !eri\ ed from parts of the gi-rminative 

 voicle. From this resulted the important a'o.-trine that, just at ill crlU, so alto 

 all nuclei of t lie animal onjanifin an- ilerirntires in an uninterrupted tfquencf, 

 the one from the e<i<j-eell and the other from if* nucleus. (Omnis cellula e ccllula, 

 omnis nucleus e nucleo.) Through these i or the 



* Radiating structures had already been observed in the yolk before this, 

 but in an incomplete manner, by different authors by GRUBE in the Hiru- 

 dinea, by DERBES and MKISSNKU in the Sea-urchin, I'.ATK in Sagitta, 



by KROHN, KOWALEVSKY, and Kri>FFi:u in A.-eidians, by I.KITKAUT in Nema- 

 todes, by BALBIANI in Spiders, and by < >I;I.LAC HI:R in the Trout. 



