250 BULLETIN OF THE 



There have been observed numerous radial phenomena, which, at various 

 times, appear in different parts of eggs and other cells. These observations, 

 to most of which my attention has been directed by Biitschli ('76, pp. 387, 

 388), are, I believe, not all based on phenomena liomologous with one another, 

 to say nothing of their being identical with molecular asters. Many of them 

 relate to the eggs of vertebrates, and the appearances have in such cases often 

 been referred to the presence of pore-canals. In how far any of them may be 

 referred to the same causes which induce the temporary radiate structures now 

 generally known as asters, can perhaps be satisfactorily determined only by 

 renewed studies. Without additional investigation it seems hardly justifiable 

 to assume, with Biitschli, that all such phenomena are identical. Among 

 the several cases which he cites, the observations of Eimer ('72", p. 219, 

 Taf. XI. Fig. 3) exhibit as strong evidence as any that they are based on the 

 study of asters ; for the thick transparent membrane about the germinative 

 vesicle is not very sharply limited from the yolk substance, the radiation about 

 the vesicle is not fully restricted to this clear zone, and the early disappearance 

 of the structure points to the unstable and temporary character of the phenom- 

 enon in this case. Still, I think it may be doubted if any of the cases 

 cited below show very close relationship with the molecular asters, since the 

 latter rapidly appear and disappear in advanced stages of the maturing egg, 

 and during segmentation. Whereas the real asters seem to point to a funda- 

 mental rearrangement of already acquired substance, the appearances in most 

 of the cases cited seem either to sustain important relations to the acquisition 

 of new material, or to represent other permanent structural differentiations of 

 the cell. 



Keichert ('56, pp. 103-124, Taf. II., III.) has described at length a peculiar 

 structure of the nutritive yolk in mature and fertilized eggs of the pike. At first 

 sight the radiate structure in this case presents a striking resemblance to molec- 

 ular stars, and more particularly to those modified spiral asters which have been 

 traced in Limax during the formation of the polar globules. There seems, 

 however, to be little ground for considering them in any way homologous. 

 Eeichert states that traces of the radiate structure are to be seen in fresh eggs, 

 although much more distinctly when hardened in acid or alcohol. In sections 

 of eggs thus treated, the striation may be seen with the unaided eye. The whole 

 nutritive yolk is traversed by light and dark radiating streaks. These extend 

 from the whole periphery, apparently converging at the centre of the yolk. 

 This central region, or vertex (Scheitel-Kegion), is not spherical ; its greatest 

 extension corresponds with the sagittal plane of the embryo. The rays, rarely 

 rectilinear, usually take a protracted S-shaped course. The streaking is some- 

 what finer at the posterior portion of the yolk than elsewhere, and is coarser in 

 the middle part of each ray than at either end. The rays are due to fine canals 

 which traverse the yolk from the periphery, where they begin with narrow 

 openings, to near the centre. Instead, however, of terminating at the centre, 

 they curve backward toward the surface. Each canal thus becomes continuous 



