588 RECOBD OF CURRENT RESEARCHES RELATING TO 



closely fitted to the yolk, with little projections on its inner surface, 

 corresponding to the vitelline pores, and a fold applied to the first 

 meridional groove. The chorion, also trans2)arent and homogeneous, 

 tightly invests the inmost membrane, like which it may be a mere 

 transformation of the outer substance of the yolk ; or is it not rather 

 a product of the granulosa, since it takes no share in the act of 

 cleavage? The chorion is separated from the inner capsule by a 

 liquid in which the egg moves freely, touching the capsule by its 

 lowest part. Frequently the egg of Triton, still within the oviduct, 

 has its vitelline sphere of an elliptic figure (persisting after extrac- 

 tion), the space about the chorion being at this time filled with jelly. 

 In Triton the liquid is often bistre-coloured and the inner capsule is 

 much thinner than in Axolotl, where its optic section displays a 

 fibrous aspect. The liquid of Axolotl at first contains brilliant 

 granules and little opaque clots which subsequently disappear. The 

 outer capsule is transparent as glass, elastic, very resistant, bluish 

 when seen against a dark ground, and homogeneous or but feebly 

 striated parallel to its surface ; elliptic in Triton, it is spherical in 

 Axolotl. Like the inner capsule it is rapidly deposited in the first 

 moiety of the oviduct. Here begins also the formation of the adhe- 

 sive layer, to be completed in the further portion of the duct. In 

 Triton this layer is thin, easily detached from the outer capsule ; not 

 so in Axolotl, where it is much softer, swelling by contact with 

 water and resembling a viscous mass. Minute depressions, arranged 

 with tolerable regularity, are often seen to mark a part of the thick- 

 ness of the adhesive layer. These are probably the stigmata left 

 by diatoms, Avhich in other places occupy spots of corresponding 

 diameter. 



I. 2. Professor Van Bambeke distinguishes seventeen stages 

 between fecundation and the exit of the embryo from the egg. 

 Stage I., ending with the beginning of cleavage, he has treated in a 

 previous memoir. Stage II., from cleavage to the commencement of 

 epiboly, is discussed in the second Part of this essay. Stages III.- 

 XVII. are here duly described. 



II. The author has studied cleavage of the egg in three species of 

 Triton {alpestris, punctatus, and palmipes), in Axolotl, Pelobates 

 fuscus, and the common toad. The latter is here referred to but 

 cursorily, for its strongly pigmented eggs offer peculiarities to be 

 explained in a future memoir. Six stages, ending with the formation 

 of the morula, are fully described and illustrated. An historical 

 sketch is added in which the results detailed are compared with 

 those of Goette, Biitschli, O. Hertwig, Scott and Osborn, and 

 Benecke : the researches of Salensky on the sterlet, with the more 

 general views of Flemming, Fol, and Mayzel, are also noticed. The 

 whole demands an attentive study. We give the author's own 

 " conclusions." 



1. Cleavage is set up by the first embryonic nucleus (der erste 

 Lehenskeim, Goette), placed in the upper hemisphere, at the limit of 

 the ccto- and endodermic segments. The axis of the egg, which 

 originally passed through the centre of the germinal depression, now 



