360 LOUIS I. DUBLIN. 



advanced than the other (Fig. 13, d). In these types also there 

 are often observed certain individual variations which are of in- 

 terest in their bearing on the relations between the nucleolus and 

 the chromosomes. A cap of deeply-staining material, showing 

 no sign of vacuoles within it, often covers one part of the struct- 

 ure. This varies in size, from the merest rim to a mass half as 

 large as the fully grown nucleolus itself. In some cases there 

 are two such caps to the same nucleolus (Fig. 14, a}. The 

 other variation consists in the frequent indentation of the outer 

 rim, which gives the appearance of disintegration on the part of 

 the nucleolus (Fig. 14, b). This view is made probable by the 

 presence in such cases of large granules, which lie within the 

 indentation and seem directly to fit into it. These conditions, 

 moreover, are found only in advanced stages of egg-development. 

 Altogether, the appearance very strikingly resembles Fig. i 3 of 



a 



FIG. 14. 



Guenther's work, '03, on the nucleolus in the maturing eggs of 

 the Echinodermata (Holothuria tnbulosa}. 



This author considers this one of the strongest elements in the 

 evidence, for the chromatic nature of the nucleolus, since the in- 

 dentation is taken to signify that the nucleolar substance has 

 broken off to become a chromosome. Such a picture as that 

 shown in Fig. 14, b, where, in an egg nearly ready for the first ma- 

 turation, some of the much concentrated chromosomes actually 

 lie within a nucleolar indentation, would most probably be inter- 

 preted by Gunther, '03, and some other authors, as very strong 

 evidence in favor of their hypothesis. Indeed, when stained with 

 haematoxylin, some of the chromosomes are in such intimate con- 

 nection with the nucleolus, that all the necessary conditions which 

 their hypothesis demands seem to be realized. Yet nothing can 

 be further from the truth. I have fortunately found such a stage 



