194 Journal of Comparative Neurology. 



to differentiate the various tissue systems very clearly and at the 

 same time perfectly preserves the most minute histological de- 

 tails. Specimens can be cut at this age without further decalci- 

 fication, though the bones of the jaws and cranium are quite 

 strongly ossified. Older specimens require more rigorous treat- 

 ment to insure decalcification. The method of study is the 

 same as that applied by von Plessen and Rabinovicz [6] to 

 Salarnandra maculata and by G. A. Arnold [i] to Pipa ameri- 

 cana; viz., reconstruction of the nerves by tracing them from 

 section to section and plotting them upon cross-section paper. 

 The degree of acuracy attainable more than compensates for the 

 painful tedium of this process. 



The surprising differences between Amblystoma and Sala- 

 rnandra serve to emphasize the importance of the gap in the 

 taxonomic series which separates the two forms. How much 

 of this difference may be due to age variation has not been de- 

 termined. It should be noted that the larvae studied by von 

 Plessen and Rabinovicz were much younger, being from 2. 5 to 

 3 cm. in length, while our specimens may be considered as in 

 most respects practically adult. It is important for the final 

 determination of the homologies that these age variations be 

 more carefully studied than has yet been done. 



The first cervical netve (1 sp.) arises by four or five small 

 ventral roots. No dorsal root was found, nor is there developed 

 a ganglion, as in Salarnandra. Immediately outside of its fora- 

 men it breaks up into a dorsal and a ventral branch. The 

 former innervates the m. longissimus dorsi of the shoulder, the 

 latter gives most of its fibres to the more ventral fascicles of the 

 same muscular system. By reason of incompleteness of the 

 series the most caudally directed fibres could not be traced to 

 their terminus. The connections of the fibres which function as 

 a hypoglossus could not, therefore, be discovered. 



The vagus aroup. The vagus and glossopharyngeus 

 originate together by five roots which blend in a common 

 ganglion. Of these roots the most cephalic and dorsal one may 

 be considered as glossopharyngeus, the others as vagus. The 

 ganglion is triangular as viewed from above and from the cando- 



