454 MOiXTGOMERY. [Vol. XV. 



Now what do these lightly staining, granular nucleoli repre- 

 sent ? In all except the seven cases here mentioned the nucleo- 

 lus was always of the deeply staining, vacuolar type, irrespective 

 of its occurrence in ova of egg pouches and of gonophores. 

 The abnormal nucleoli, with one exception, were found in the 

 largest ova of the egg pouches. Types intermediate between 

 the two are represented in Fig. 210. Conklin and Brook's 

 observations, which I can corroborate, show that a number of 

 ova are produced in an egg pouch, but that only one of these 

 passes into a gonophore, and there develops into the ripe ovum, 

 while the others remain behind in the egg pouch and do not 

 reach maturity, but degenerate. I would hold that the abnormal 

 nucleoli described by me are degenerating nucleoli of degener- 

 ating ova. All the facts seem to favor such an explanation. 



The cytoplasm of the youngest egg cells appears finely granu- 

 lar (it may be an alveolar meshwork). In the largest it was 

 coarsely vacuolar, especially near the center of the cell ; I find 

 no evidence of yolk. Conklin and Brooks evidently mistook 

 the vacuoles of the cytoplasm for yolk globules. 



No chromatin threads were apparent in the smallest germinal 

 vesicles (Figs. 204-206), but only a fine granulation in the 

 nuclear sap ; chromatin threads make their appearance gradu- 

 ally in the larger ova (Figs. 207, 209, 211) and stain more 

 intensely as they increase in number and size. Each thread 

 often has the form of a chain of transversely placed discs ; or 

 sometimes it would seem to consist of a large number of short 

 fibrils, placed at right angles to a common longitudinal axis, as 

 is the structure of the chromosomes of the Selachian egg. 

 These threads usually make their first appearance in the neigh- 

 borhood of the nucleolus, from which they sometimes radiate 

 outwards ; only in the largest nuclei are they more generally 

 distributed throughout the nucleus. This fact might show a 

 physiological relation between these two structures. But there 

 is in all probability no genetic connection between the two ; 

 rather, the chromatin threads are built up of the minute micro- 

 somes found in the nuclear sap of the smaller ova. But the 

 formation of the chromatin threads must be determined by the 

 investigator who has more abundant material at his disposal. 



