Prof. Valentin's Report on the Progress of Embryology, 371 



of a principal cell gives the stimulus to the formation of the 

 embryo. Fecundation thus consists in the imbibed seminal 

 fluid stimulating the germinal spot to the cell-formation, ac- 

 cording to the type of cells in cells. But many more cells 

 are formed than remain ; the outer layers being constantly 

 absorbed. 



7. The furrows known to be presented by the yelk arise from 

 the formation of cells (see Repertorium, v. 306). Their pre- 

 sence in Fishes was established by Rusconi, in Mammals by 

 Barry. In Birds they may either entirely fail, or, as is more 

 probable, be limited to the germinal membrane and not ex- 

 tended to the yelk. 



8. The rotation of the yelk or of the embryo in the ovum, 

 previously observed in invertebrated animals and in Batrachian 

 reptiles^ is also found to take place in fishes and in mammalia. 

 RuscoNi perceived this rotation fifty hours after fecundation 

 in ova of the pike ; so that it is thus met with Avhere there is 

 a circumscribed germinal membrane. In the rabbit it was 

 seen by Barry, although he remained in doubt as to the na- 

 ture of the rotating body, which was determined by Bisciioff. 

 The latter described also vibrating cilia on the superficial 

 cells. It now remains a point of especial interest to extend 

 the observation to classes which otherwise do not exhibit 

 ciliary motion, for instance, the Crustacea. 



9. Of the other structures of the [Graafian^ follicle which pass 

 out [of the ovary^ along with the ovum, the tunica granulosa^ 

 and retinacula [discus proligerus^ undergo liquefaction, wliile 

 within the zona there arise concentric formations of membranes 

 and fluid or semifluid rings. According to Barry this forma- 

 tion amounts to from four to five membranes, the attenuation 

 of the zona, above mentioned, soon disappears. The chorion 

 is not formed out of the zona, but out of cells, which arise in 

 the tube, and are laid down around the metamorphosed struc- 

 tures. P. 250. 



[Professor Valentin then proceeds to give details of the 

 observations of Dr Barry, the principal of which are the fore- 

 going nine. These details will be found in the Philosophical 

 Transactions for 1839 and 1840. Abstracts of them have 

 been already furnished by this Journal.] 



