EMBRYOLOGY OF CLEPSINE. 237 



this time. The ring-substance is coloured brown by the osmic 

 acid and carmine. The unshaded portion lying below and at 

 both sides of the ring is a zone of protoplasm^ which contains 

 yolk-granules, but no large yolk-spheres. It is this zone which 

 forms the two white ring- borders seen on living eggs. 



e. Primary Cleavage-nucleus. — Lying a little excentrically 

 towards the oral pole is the primary cleavage-nucleus. The 

 nucleoplasm is more strongly colored in the centre around the 

 pronucleolar bodies than at the edges. These nucleolar cor- 

 puscles are several times larger than in the preceding tig. In 

 fig. 67, J., two of these bodies (= 0-35 mm. diam.) are seen 

 with their concave sides applied to the third nearly round body 

 (=.03 mm. diam.). They are sharply outlined, but only slightly 

 stained with carmine. Between the ring and the cleavage 

 nucleus (G) a line, more highly colored than the rest of the 

 yolk, is sometimes seen. This line, judging from its position 

 and direction, I interpret as the path^ taken by the female pro- 

 nucleus towards the male pronucleus. The three corpuscles in 

 the centre of tlie nucleus are undoubtedly the pronucleoli 

 de-scribed in fig. (36, the two uppermost being the female pronu- 

 cleoli, and the lower one the male pronucleolus. The longer 

 axis of the nucleus in this st.ige is in every instance at right 

 angles to the axis of the egg, whereas at the moment of union 

 of the pronuclei, the longer axis was found parallel with that of 

 the egg, and a little later (fig. 66, /) inclined about 45*^. 

 Whether anything occurs here comparable with the rotation 

 described by Auerbach (^a^) for Ascaris, I am unable to say. 



The advancement of the rings will be easily understood by 

 referring to figs. 68 — 71, Pi. XIV. The calotte (cal.) reaches its 

 inimimum dimensions about one hour after the first ring appears 

 (tig. 71, 2 h. 30 min.). As the calotte diminishes, the oral 

 ring concentrates and deepens until it arrives at the cordate form 

 seen in fig. 71. The lower ring, as it concentrates covers the 

 aboral pole more and more, forms a shallow disc (fig. 69), and at 

 length presents the oblong oval form of tig. 71. It is quite 

 certain that both rings are composed of essentially the same 

 substance. It is impossible to distinguish on the living egg the 

 substance of one ring from that of the other ; and both, when 

 treated with osmic acid, alcohol, and carmine, present the same 

 characteristic shades of brown, varying according to the in- 

 tensity of the acid action, between a dark brown and the lead- 

 grey first spoken of in connection with the germinal vesicle. 



Wiien hardened in alcohol, and coloured with carmine, both 

 the rings and the nucleus are deep red. It is therefore probable 

 that the ring-substance is nuclear material, or something very 



^ Auerbach saw sucli a Stras>>e iu the egg of Ascaris uigrovcuosa (a^^). 



