PAPERS ON BIOLOGY AND AGRICULTURE 135 



as Hyla, the tree toad and the earlier stages of Rana, as 

 described by Gaupp, a conclusion entirely warranted, it 

 would appear that the roof of the capsule is but a lateral 

 chondrification of the dorsal margin of the planum ver- 

 ticals So the entire roof of the capsule, as well as the 

 planum verticale, above described, is but a further chron- 

 drification of the single median ethmoidal column of the 

 earlier larval stage, together with certain additions from 

 the planum ethmoidalis. 



The foregoing comparison shows that there is a defi- 

 nite relationship between the younger and the later 

 stages. It was found that the two trabeculae, separated 

 by the internasal space in the younger embryo, were 

 united, later forming the floor of the capsule in the older 

 one. The planum basale, here as well as in the earlier 

 stage, forms the floor of the cavum cranii ; also the cornua 

 remain, but have assumed a different position. 



It follows that the nasal capsule of the younger toad is 

 but a further development of those structures appearing 

 in my earlier larva. Development is a continuous pro- 

 cess, and in the final result a more specialized but reduced 

 capsule is attained. 



According to the zoological classification of Amphibia, 

 this class is divided into four orders: Anura, Urodela, 

 Gymnophiona, and Stegocephala. This paper is con- 

 cerned only with that class Anura and its subdivisions, 

 and upon the evidence of the nasal capsule it would ap- 

 pear that the existing order of Amphibian classification 

 is entirely supported by this investigation. 



EXPLANATION OF PLATE. 

 Fig. 1. Anterior view of model of nasal capsule of Bufo americana, 



14 mm. total length. X54. 

 Fig. 2. Posterior view of same model. 

 Fig. 3. Ventral view of same model. 

 Fig. 4. Dorsal view of same model. 



Fig. 5. Transverse section through posterior part of nasal capsule. 

 Fig. 6. Lateral view of model of Fig. 1. 

 Fig. 7. Transverse section through planum basale and muscularis 



process of the quadrate. 

 Fig. S. Transverse section through planum basale and olfactory nerve. 

 ALC Alisphenoid cartilage PE Planum ethmoidalis 



CC Cavum cranii PB Planum basale 



CT Cornu trabeculae PP Pterygoid process 



EC Ethmoidal column PPT Pons pterygoidei 



MPQ Muscularis process of the PT Pons trabeculae 



quadrate QEP Quadrato-ethmoidalis process 



NOR Nasal organ T Trabecula 



OLF Olfactory nerve 



