60 Papers from the Marine Biological Laboratory at Tortugas. 



The fact that the early segmentation stages give a chromosome count in 

 the prophase of approximately 36 indicates that the 18 bilobed chromo- 

 somes of the first maturation prophase are mostly, if not entirely, bivalents. 

 Moreover, their double character is occasionally plainly evident (figs. 64, 65). 

 However, since synapsis could not be observed, no conclusive evidence 

 appears as to the valency of the chromosomes, nor as to whether the chromo- 

 somes coupled endwise or sidewise, nor in which direction the condensa- 

 tion occurred to give rise to the bilobed form ; hence no positive statement 

 is justified as to whether the reduction is quantitative or qualitative. If the 

 chromosomes fused side by side in synapsis and the bivalents were so trans- 

 formed into a bilobed body that each globe can be represented by AB, then 

 the double longitudinal division effects a true reduction, and the resulting 

 chromosomes are /Ts and B's. If one globe represents A and the other B, 

 then the resulting chromosomes are AB's. Similar possibilities result from a 

 double longitudinal division if the synapsis was endwise. 



FUNCTION OF THE NUCLEOLUS. 



As to the function of the nucleolus in the germinal vesicle, besides giving 

 rise to the chromosomes, various opinions are held by different writers, some 

 ascribing to it an incidental role in conjunction with chromosome formation, 

 others a very definite role exclusive thereof. I shall not undertake to give a 

 full discussion of so complicated and difficult a subject. I desire merely to 

 call attention to a few of the most divergent views in regard to this enig- 

 matical cell-constituent and harmonize my own observation with one or the 

 other of these. 



Pfitzner (1883), basing his opinion on his investigation of the ectodermal 

 cells of Hydra, makes the generalization that the nucleolus has merely a 

 passive function in mitosis : " die einer aufgespeicherten Nahrungs-materials 

 zur Neubildung von Chromatin." He terms the nncleolar substance " pro- 

 chromatin," since he finds that in mitosis it changes into chromatin. 

 Schneider (1901) thinks that the large nucleoli of echinoderm eggs are 

 but reserve masses of chromatin. The experiments with artificially fer- 

 tilized echinoderm eggs by R. Hertwig (1895) and Wilson (1901) seem to 

 confirm the validity of Schneider's view, at least under certain conditions. 

 Rhumbler (1893) says: "Mir scheinen die Binnenkorper (nucleoli) Reser- 

 vestoffe darzustellen, die fur Zeit aufgespeichert werden, wo die Theilung 

 eine grosse Zunahme des Vererbungs Apparates bez. des Idioplasm im Sinne 

 Weismann's erfordert, wo aber diese Stoffe nicht rasch genug durch die Zell- 

 membran hundurch Nahrung finden konnen." 



Hacker (1895) states that in JEquorea .and in various annelids and echino- 

 derms " the nucleolus is cast out bodily into the cytoplasm, afterwards lying 

 there for some time as a ' metanucleus ' before degenerating. In these cases 

 the chromosomes are formed independently of the nucleoli ... it seems 



