428 MONTGOMERY. [Vol. XV. 



assimilated yolk spherules. Thus, as we find in the cytoplasm 

 first yolk balls, then their fragments, and finally the mature yolk 

 spherules, so in the nucleus the first generation of nucleoli 

 are assimilated yolk balls and their fragments, while the small 

 ones of the second generation are derived from the only yolk 

 elements then present in the cytoplasm, namely, yolk spherules. 

 The nucleoli of the first generation also differ from those of 

 the second, at the time of the first appearance of both, in 

 their manner of staining ; so that they would seem to differ 

 chemically from each other. 



Nuclear structures of problematical significa7tce. — In only 

 one out of the three individuals of this worm studied were the 

 following remarkable structures to be observed, though the fixa- 

 tion method of both of the other individuals was exactly the 

 same. These bodies first appear in ova of the second nucleolar 

 stage, but here show always the same typical structure, so that 

 I can say nothing as to the manner of their first formation. In 

 preparations stained with haemato.xylin and eosin they are 

 colored by the former stain a little more deeply than the 

 nuclear chromosomes, so that they stand out sharply in the 

 nuclear substance (N. Bd., Figs. 122-139). The smaller ones, 

 i.e., those of the younger germinal vesicles (Figs. 122-126), 

 are finely granular, though whether they each consist of a mass 

 of fine granules or of homogeneous ground substance in which 

 granules are distributed, I cannot determine. In the larger 

 nuclei they often appeared wholly homogeneous (Fig. 132). 

 In shape they are usually nearly spherical, with a sharp outline, 

 which may or may not represent a limiting membrane ; the 

 larger ones are often more irregular in form (Figs. 132, 133, 

 139). In the smaller nuclei they are as a rule, but not always, 

 smaller than in the larger ones ; in the smallest nuclei in which 

 I have found them there is only one of these bodies to a 

 nucleus ; while in the larger nuclei they are not only larger, 

 but also there may be from one to four of them in each nucleus. 

 In only one small nucleus were three of them present (Fig. 

 128). In two cases, both larger nuclei, I found division stages 

 of these bodies : in the one case (Fig. 131) the body was ovoid 

 in outline, with a shallow constriction at right angles to its 



