570 BULLETIN OF THE 



the various rays of the aster which remains in the yolk after the elimination 

 of the second polar globule are amassed and disappear as such ; but their 

 reunited substance, especially that of the bipolar filaments, forms a small cor- 

 puscle, transparent and difficult to see in the living egg, but very apparent 

 when treated with osmic acid and carmine. It is at first immovable, and in- 

 creases gradually in volume ; afterwards it moves from the surface, at first 

 slowly, and then more rapidly. At the side of this arise other pale spots, which, 

 at first very small, grow rapidly, approach the first one, following its centripetal 

 movement, and finally fuse with it. The impression conveyed by this descrip- 

 tion is that only the first pale spot arises directly from the spindle fibres. The 

 others are not constant in their position. Treatment with acids causes these 

 spots to appear like nuclei, and one distinguishes a very irregular enveloping 

 layer ; the smaller the nucleus, the thicker the layer. Within these small nuclei 

 are one or several nucleoli, which grow at the same time as the nucleus. They 

 are surrounded with rays which increase rapidly in extent during the growth 

 of the nuclei, but disappear when the pronucleus becomes stationary. If this 

 account of the origin of the female pronucleus is accurate for Asterias, there 

 must be an important diff"erence between it and Limax, for in the latter I am 

 very sure there are no accessory nuclear vacuoles which are entirely indepen- 

 dent of the spindle fibres. 



He says these changes transpire the same, whether the eggs have been fecun- 

 dated or not, except in regard to the position of the polar globules (inside or 

 outside the vitelline membrane) ; but they occur a little more rapidly when the 

 eggs have been fertilized. 



The maturation of the eggs of the sea-urchin offers little additional informa- 

 tion. The amphiaster and the single polar globule are larger in proportion to 

 the size of the egg than in Asterias, and once two rows of granules (zones of 

 fibre thickenings) were seen, one near each pole of the globule. 



The germinative spot is wanting in the very young as well as in the maturer 

 eggs of a Sagitta, which the author names S. Gegenbauri. There are other 

 species of this genus in which the nucleolus is present. The office filled by 

 the nucleolus in the development of the ovule, the author therefore concludes, 

 cannot be one of primary importance. The place of the large germinative 

 vesicle, which has grown smaller and disappeared, is occupied, before the exclu- 

 sion of the egg, by a compact corpuscle with stellate borders, in the interior of 

 which is to be distinguished, after treatment with very weak solutions of osmic 

 acid and bichromate of potash, a vertical row of small refringent grains, the 

 optical section of the plane which the granules constitute. This phase resembles 

 that one which in Asterias was the cause of the author's denying the identity 

 of the first amphiaster and that from which the first polar globule arises. The 

 two globules are produced successively, and in fecundated eggs are restrained 

 by the vitelline membrane, being forced into a depression which they cause in 

 the surfiice of the yolk, but in non-fecundated eggs they are detached, and 

 are retained only by the mucilaginous envelope. Here also these changes all 

 transpire more slowly in eggs that have not been fecundated. 



