424 O. LARSELL 



compared with the olfactory nerve in that form. He finds it 

 also in Cyclostomes and states that in Bdellostoma the nerve 

 presents an intermediate stage, as respects its size and relations, 

 between Amphioxus and the selachians. He calls attention to 

 the distinction between the vomeronasal nerve, which he terms 

 the 'nervus septalis' and the olfactory nerve, and suggests a new 

 classification of the cranial nerves in which the nervus terminalis 

 would be number I, and, with the 'nervus septalis', would be 

 added to the list of twelve cranial nerves usually recognized. 

 The nervus terminalis is considered a sensory nerve which has to 

 do with a group of chemical sense organs, and is related physi- 

 ologically to the vomeronasal (his septal) nerve. The conclusions 

 are reached from a study of Amphioxus and cyclostomes. Doctor 

 Ayers believes that in higher forms the nerve has undergone con- 

 siderable modification due to changes in head structure. 



I am under great obligation to Doctor Ayers for opportunity 

 to read his manuscript prior to publication and for permission to 

 make use of his observations. He also afforded me opportunity 

 to read Van Wijhe's paper, which I had not previously seen. It 

 is a pleasure to express here my sense of indebtedness to him. 

 My acknowledgments are also due Prof. William A. Locy, of 

 Northwestern University, under whose direction the general 

 problem was originally begun and who has since continued his 

 interest. 



MATERIAL AND METHODS 



Embryos of the painted turtle (Chrysemys marginata) were 

 used. Most of these had been fixed in a formol-bichromate- 

 acetic fluid, some in formalin of 10 per cent, others in Tellyes- 

 niczky's fluid, and a few living embryos were obtained and pre- 

 pared by the Cajal and the Vom Rath methods. 



Stages beyond 10- to 11-mm. carapace length had become 

 chitinized to such an extent in the rostral region that intact 

 serial sections could not be obtained. Chiefly for this reason, 

 the present contribution is confined to a description of the nervus 

 terminalis in embryos up to 11-mm. carapace length (about 17 

 mm. greatest length. 



