52 Journal of Comparative Neurology. 



eal has evidently changed. Instead of lying midway between 

 the terminal points of the diencephalon, the pineal is included 

 in the caudal one-fourth. The pre-pineal portion retains ap- 

 proximately the same thickness, but grows rapidly forward, 

 keeping pace with the roof of the prosencephalon. 



While the post-pineal portion becomes depressed and 

 thickens and is rapidly encroached upon by the fibers of the 

 post-commissure. At this stage important changes are also 

 taking place in the pineal itself. It becomes irregularly lobed, 

 thickens and projects forward. 



Thus the conditions which are shown to be permanent in 

 Amphibia, are transitory in the amniate vertebrates. In trout 

 fry of nine days old, the post-pineal segment is thrust under by 

 invagination forming the torus, in which process the post-com- 

 missure is also sharply plicated. 



It would appear that the b(_Miy fishes are more closely 

 allied, in this respect, to amphibians than are the ganoids. 



In duck embryos of a somewhat later stage the entire roof 

 of the diencephalon has undergone important morphological 

 changes. For convenience, the following nomenclature will be 

 used: i, post-commissure; 2, pineal recess; 3, pineal; 4, su- 

 pra-commissure; 5, post-paraphysis ; 6, vellum transversum ; 

 7, pre-paraphyses, with a possible post- and pre-plexus. In 

 this stage the pineal recess does not appear, having been partly 

 encroached upon by the post-commissure, and partly absorbed 

 into the pineal. 



The postparaphysis extends from the supra-commissure to 

 the velum and is somewhat corrugated. The velum separates 

 the post- and preparaphyses and joins the roof and base of the 

 cephalic limit of the diencephalon. The preparaphysis unites 

 the velum with the prosencephalon. From the cephalic side 

 of the velum the preplexus has developed and enters the pro- 

 sencephalic ventricles. 



The epiphysis at this stage projects cephalad and forms 

 several diverticles. This process goes on as development con- 

 tinues, until the base or undivided portion of the epiphysis be- 

 comes almost disconnected from the third ventrical, or, in other 



