144 J- Moore, 



The nucleolus ne' somtimes appears to be connected in some way 

 with the formation of a part of one of these, or at any rate it seems 

 to become blended with one of the eight chromatic masses. I think 

 it probable however that the great mass of this structure is absorbed 

 into the cytoplasm. It is generally supposed that the nucleolus is 

 genetically different from the remaining nuclear constituents, and in 

 vegetable histology the opinion has led up to the conception that the 

 nucleolus has little if any connection with the ordinary chromatic 

 elements, but this I very much doubt. ^) Julin in the above-cited 

 treatise has homologised ^) the nucleolus of Ovogonie with the macro- 

 nucleolus of the Ciliata, and that of the spermatogonie with the ordi- 

 nary centrosome. However this may be, I am personally unable to 

 find any greater differences than those produced by transitory physical 

 causes, between the nucleolus of the mammalian spermatocyte and the 

 chromosomes. The structure appears to originate as an anastomosis 

 of the fine chromatic reticulse, and to persist late into the prophases 

 of the division merely by virtue of its greater condensation. This 

 condensation I believe to be the sole cause of the difference in staining 

 capacity which it certainly exhibits during the latter part of its existence 

 (I refer only to the nucleolus of the rat). 



Each of the eight chromatic condensations or chromosomes, when 

 closely examined, is seen to be a loosely aggregated loop (Fig. 3) 

 whose staining material is present in the form of innumerable micro- 

 somes. These microsomes are apparently suspended in a hyaline non- 

 staining substance, fine strands of which stretch from chromosome to 

 chromosome, producing the „goupillon" appearance; and on these slender 

 tracts odd microsomes are often found, as if they had been caught 

 while gradually collecting into differentiated areas already occupied by 

 the growing chromosomes. As the phase approaches its completion, 

 the nuclear membrane appears rather rapidly to give way, the chromatic 

 loops being shot outh with more or less suddenness and force. Tlje 

 rapidity with which these changes take place renders cells presenting 



*) See Zimmermann, Privatdozent der Botanik, Beiträge zur Morphologie nn« 

 Phj'siologie der Pflanzenzelle. Tübingen. Band IT. Heft 1. 

 ■-) Loc. cit. p. 36. 



