Volume //.] June, 1901. \_No. 6. 



BIOLOGICAL BULLETIN. 



[From the Zoological Laboratory of the University of Pennsylvania.] 



THE INDIVIDUALITY OF THE GERM NUCLEI 



DURING THE CLEAVAGE OF THE 



EGG OF CREPIDULA. 



EDWIN G. CONKLIN. 



HAECKER ('92) and Riickert ('95) have made known the 

 interesting fact that the germ nuclei of Cyclops do not fuse 

 but preserve their individuality throughout a considerable por- 

 tion of the cleavage of the egg. Herla ('93) and Zoja ('95) 

 have shown that the paternal and maternal chromosomes of 

 Ascaris remain distinct at least as far as the 12-ceil stage. 

 These observations are of the greatest significance and, so far 

 as they go, establish Boveri's hypothesis ('91), "that in all cells 

 derived in the regular course of division from the fertilized 

 egg, one-half of the chromosomes are of strictly paternal 

 origin, the other half of maternal." So far as I am aware, 

 similar observations have not hitherto been made in the case 

 of other animals. 1 



1 Riickert calls attention to the fact that partially cleft nuclei are found in 

 the figures of various authors, particularly those of Fol ('79) on Toxopneustes, 

 of Bellonci ('84), and of Kolliker ('89) on Siredon. Of course no one of these 

 observers has interpreted these figures as showing the independence of the germ 

 nuclei, and some of the figures referred to by Riickert probably do not show this 

 phenomenon. For example, only one of Fol's figures (PI. VII, Fig. 7) shows a 

 dual nucleus, while the figure in Kolliker's text-book (Fig. 36) is probably a case 

 of the indentation of the nuclear membrane opposite the centrosomes in the early 

 prophase, a thing which frequently happens. Bellonci's Figs, i and 20 show an 

 indentation on one side of the nucleus which may correspond to a division between 

 the germ halves, though this must be regarded as more or less doubtful. 



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