STRUCTURE AND DEVELOPMENT OF VERTEBRATE OVAllY. 395 



initive ova into a single mass or syncytium ; though of course, 

 the several separate ova of a nest may originally, as Semper 

 believes, have arisen from the division of a single ovum. In any 

 case there can be no doubt that the nests of separate ova increase 

 jAn size as development proceeds ; a phenomenon which is more 

 reasonably explained on the view that the ova divide, than on the 

 view that they continue to be freshly formed. The same holds true 

 for the nests of nuclei and this, as well as other facts, appears to me 

 to render it probable that the nests grow by division of the nuclei 

 without corresponding division of the protoplasmic matrix. 

 I cannot, however, definitely prove this point owing to my having 

 found nests, with distinct outlines to the ova, as large as any 

 without such outlines. 



Tlie nests are situated for the njost part near the surface of 

 the germinal epithelium. The smaller ones are frequently 

 spherical, but the larger are irregular in form. The former are 

 about 0'05 mm. in diameter; the latter reach 0*J mm. 

 Scattered generally, and especially in the deeper layers, and at 

 the edges of the germinal epitheliuui, are still unmodified or only 

 slightly modified primitive ova. These unmodified primitive ova 

 are aggregated in masses, but in these masses the outlines of 

 each ovum, though perhaps less clear than in the earlier period, 

 are still distinct. 



When the embryo reaches a length of 7 centimetres, and 

 even in still younger embryos, further changes are observable. 

 In the first place many of the modified nuclei acquire fresh 

 characters, and it becomes necessary to divide the modified nuclei 

 into two categories. In both of these the outer boundary of the 

 nucleus is formed by a very delicate membrane, the space within 

 which is perfectly clear except for the granular body. In the 

 variety which now appears in considerable numbers the granular 

 body has an irregular star-like form. The rays of the star are 

 formed of fibres frequently knobbed at their extremities, and 

 the centre of the star usually occupies an excentric position. 

 Typical examples of this form of modified nucleus, which may 

 be spoken of as the stellate variety, are represented on Plate 

 XVill, fig. 17 ; between it and the older granular variety there 

 is an infinite series of gradations, many of which are represented 

 on PI. XVIII, figs. 12, 11, 15, 16. Certain of the stellate nuclei 

 exhibit two centres instead of one, and in some cases, like that 

 represented on PL XVIII, fig. 19, the stellate body of two 

 nuclei is found united. Both of these forms are possibly modi- 

 fications of the spindle-like form assumed by nuclei in the act of 

 dividing, and may be used in proving that the nests increase in 

 size by the division of the contained nuclei. In addition to the 

 normal primitive ova, a few of which are still present, tlure arc to 



