PAPERS OX BIOLOGY AND AGRICULTURE 123 



work was done in the Knox Biological Laboratory, and 

 the writer regrets very much that earlier and later stages 

 were not available so that a more complete study of the 

 development of the capsule could be made. 



These embryos, measuring respectively 75mm. and 

 63mm., have been sectioned and studies made upon the 

 development of the nasal capsules and their relation to 

 the nasal organs. Keconstructions by the Born wax- 

 plate method have been made of these structures in both 

 embryos. Drawings of these models and the sections oi 

 the nasal organs have been made showing the relation to 

 the capsule itself. 



This work was carried on under the supervision of Dr. 

 G. M. Higgins, to whom the writer is indebted greatly, 

 not only for his invaluable assistance during the prepara- 

 tion of this paper, but also for his inspiring influence. 



In the younger of the two embryos, that of 63mm. total 

 length, chondrification is not complete, and the deeper 

 structures of the head are exposed through large gaps 

 in an incomplete chondrocranium. The nasal capsules 

 with which this Investigation is primarly concerned, 

 consists in this stage of two curving plates of cartilages, 

 connected to each other in the median line. 



The trabeculae, which form the floor of the chondro- 

 cranium in the brain region, unite anteriorly to form a 

 prominent bar of cartilage, the septum nasi, which sepa- 

 rates the two nasal organs from each other (Figs. 2, 4). 

 This structure probably represents a prism of the paired 

 trabeculae which form so important a part of the nasal 

 capsules of the amphibia. Anteriorly this septum nasi 

 expands along its ventral margin into a pair of small 

 perpendicular plate-like cartilages, which extend later- 

 ally a considerable distance and end in prominent pro- 

 cesses ventral to, but in a plane with the external naris 

 (Figs. 1, 3). It would appear that these cartilages are 

 remnants of primitive cornu trabeculae, so prominent in 

 capsules of lower forms, but have lost in the reptiles all 

 association with the nasal organ itself, being consider- 

 ably ventral and anterior to the nervous structures. 



From the anterior third of the dorsal margin of the 

 septum nasi, two curving plates of cartilages, separated 



