MUSEUM OF COMPARATIVE ZOOLOGY. 441 



alcohol is an artificial condition, as Bambeke maintains. The shrivel- 

 ling of the vesicle is accompanied by a centripetal migration of the 

 nucleoli. Further changes take place only in the early spring. The 

 vesicle then approaches close to the dark pole, and ultimately exchanges 

 its much lobed and folded outline for that of a flattened curved disk. 

 A pigment zone surrounds this disk, — in R. temporaria even on the 

 superficial aspect, — and is continuous with a pigment stripe extending 

 a short way toward the centre of the yolk. The deep end of this stripe 

 is swollen, and embraces a circular clear space connected with a funnel- 

 shaped similar space immediately under the germinative vesicle. No 

 nuclear structure is to be found in the circular spot. The whole re- 

 sults from the closing together of the pigment zone which surrounded 

 the vesicle whan the latter migrated toward the surface, and therefore 

 indicates the course it had taken. The method of the ultimate disap- 

 pearance of the vesicle, which probably takes place about the time the 

 eggs are set free in the abdominal cavity, was not discovered. All the 

 eggs from the body-cavity and the oviduct exhibit the same condition, — 

 the peculiar distribution of pigment matter named by Bambeke clavi- 

 form figure, and the hemispherical clear mass of yolk at the peripheral 

 end of the latter, but not the least thing, within or without the yolk, 

 that could be considered as a remnant of the germinative vesicle. The 

 vesicle is not eliminated in the Amphibia, as in the trout, but is dis- 

 solved without recognizable remnant, and mingled with the yolk be- 

 fore fecundation. This takes place, however, only after the vesicle has 

 reached the surface. 



Finally, Hertwig discusses at some length (pp. 68-71) the significa- 

 tion of the polar globules. The three principal sources of confusion 

 in their interpretation have been: (1.) an exaggerated estimate of the 

 frequency of their occurrence ; (2.) a mistaken identification of widely 

 different structures, in that every formed particle of protoplasm between 

 yolk and egg membrane has been considered polar globule ; and (3.) the 

 assumption of a genetic connection between two often contemporaneous 

 phenomena, — the disappearance of the germinative vesicle in the mature 

 egg, and the appearance of formed bodies outside the yolk. Since it 

 has been shown that the regressive changes of the germinative vesicle 

 and the metamorphosis of the germinative dot into a spindle-shaped 

 nucleus take place in the ovary a long time before the exclusion of the 

 eggs, and that it is only after this that the formation of polar globules 

 takes place, it is evident that the processes stand in no relationship ; 

 they must be separately estimated. 



