1897] MICROSCOPICAL JOUKNAL. 311 



the Amphibia, having a small mesal portion. With its 

 growth caudad it revolves, so to speak, about a fixed 

 point, carrying the thin membranous wall before it, and 

 thus forms the folded metaplexus of the adult. The old- 

 est embryo shows this admirably. 



13. The floor of the oblongata undergoes wonderful 

 changes, from a comparatively thin-Avalled condition in 

 the youngest embryo, through one in which series of 

 rounded thickenings occur, these in turn becoming uni- 

 ted, as the carapace developes, to form the continuous 

 thickened floor of the oldest embryo. 



From the above it is seen that partial answers to the 

 questions mentioned are now possible. 



(a.) The general form of the brain of the soft-shelled 

 turtle wherein it differs markedly from the other descri- 

 bed turtles is only acquired after the embryo has the 

 external appearance of the adult, the great relative 

 growth of the cerebrum and cerebellum taking place 

 after that period. (Sec. 1, 2.) 



(b.) The union of the olfactory lobes across the meson 

 and the large caudal growth of the cerebellum seem to be 

 characteristic of this group of turtles, and it was found 

 that both are of late development, (Sec. 3, 12.) 



(c.) The broad distinctions between the bird and rep- 

 tile brain are, that the latter possesses a medicommissure 

 and a solid roof to the geminums; in the soft-shelled tur- 

 tle both of these features arise in the late embryo. 



That is, in the brain not only those features which 

 distinguish the group of turtles, but which most eviden- 

 tly distinguish birds from reptiles, arise in this turtle 

 about the time the external form is characteristic of the 

 genera. The brain, however, lags somewhat behind the 

 body in assuming characteristic features. 



Other questions arose as to the appearance of the nidi 

 and their relation to sulci, which cannot yet be answere 

 conclusively. 



