Ookinesis in Cerebratiilus Lacteiis. 359 



hsematoxylin or iron-hsematoxylin. After the germinal vesicle has 

 faded the denser part becomes a hollow sphere (PI. I, Figs. 12, 14; 

 PI. IV, Fig. 60). It usually disappears at a late prophase of the 

 first maturation mitosis, although sometimes it may be seen as late 

 as the metaphase, it being taken up into the equatorial plate like 

 the chromosomes. 



The smalk'r ])]asni()S()nu's \ary in number, usually three or four, 

 sometimes as many as nine (PI. I, Fig. 1). These nucleoli are situ- 

 ated just beneath the nuclear membrane. They are about one-fifth 

 of the larger in diameter, and sometimes are composed of denser 

 and thinner parts as in the larger one (PI. I, Fig. 11). They 

 gradually dwindle (PI. I, Fig. 10) and, when the germinal vesicle 

 has faded, no trace of them can be found. 



A chromatin mass, composed of chromatin spherules, is always 

 found close by each of the smaller nucleoli and three or four of 

 them are associated with the larger one. Sometimes one or two 

 chromatin spherules are found imbedded in the latter (PI. I, Fig. 

 12).^ 



The chromatin mass stains purple with Auerbach's fluid. At the 

 beginning of the maturation, when the nuclear membrane is fading, 

 pa7-i passu with the dwindling of the smaller nucleoli, the chromatin 

 masses resolve into smaller spherules. They become greener and 

 greener when stained with Auerbach's fluid. After the smaller nuc- 

 leoli have completely disappeared there are found some two dozen of 

 chromatin granules of irregular shape staining brilliant green with 

 the above fluid (PI. I, Fig. 14). The number of the chromatin blocks 

 is not constant. Of these only eighteen (PI. I, Fig. 15) go to the 

 equatorial place of the first maturation figure and become the defi- 

 nite chromosomes. The rest of the granules disa]")pcar without giv- 

 ing rise to the chromosomes (chromatin diminution) J The rest of 



*In the egg treated with a solution of CaCl^ (Yatsn, '05, p. 2i¥)) the chroiuo- 

 somes arise in the germinal vesicle as fine threads resembling those found in 

 the segmentation nucleus {V\. I. Tig. 1.3) (cf. Wilson '07a, pp. 572-.575). 



'In Cei-edratnlus murglnutuH the reduced number is sixteen (Coe. '99, p. 441; 

 Kostanecki. '02. p. 272). It should ho noted that in some eggs nineteen chromo- 

 somes are found instead of oigliteen (PI. 1. Fig. 10). There are three possi- 

 bilities to account for this irregularity in the number of chromosomes: a, 



