344 C. JUDSON HERRICK 



The great difficulty in getting adequate histological preparations 

 of these brains is largely responsible for this situation ; and, further- 

 more, the tissues themselves are organized in a very primitive 

 fashion, so that, when the functional analysis is finally effected, 

 the neurones of the gray substance can be separated into function- 

 ally defined groups with far less precision than in the brains of 

 most fishes and amniote vertebrates and the localization pattern 

 is found to be somewhat different in plan from that of the more 

 highly differentiated brains. 



The present study is based upon the brains of several species of 

 lower urodeles, particularly Necturus, and a more detailed exami- 

 nation of that of Amblystoma tigrinum (Green), Both larval 

 and adult stages have been studied, but this description will be 

 confined to the larva of Amblystoma except when explicitly 

 stated to the contrary. For most of this material I am indebted 

 to the generosity of Professors Paul S. McKibben and Charles 

 Brookover, who very kindly placed at my disposal a large number 

 of microscopic sections of larval and adult brains prepared in 

 diverse ways. 



Kingsbury ('95) has given us a very exact and illuminating 

 account of the medulla oblongata of adult Necturus and I have 

 recently contributed ('14) a more detailed description of the cere- 

 bellum and its connections in this species. Many other authors 

 have added important, though more fragmentary, data on the 

 oblongata of urodeles. Kingsbury's description of the medulla 

 oblongata and cranial nerves of Necturus is found to apply with 

 very minor changes to larval Amblystoma. His account is based 

 chiefly on Weigert preparations and, since in adult Necturus and 

 in the larval stages of Amblystoma (where the architectural 

 pattern is more simple than in the adult) many of the most impor- 

 tant tracts are nearly or quite non-myelinated, further informa- 

 tion is required regarding the connections of these non-myelinated 

 fibers and the intrinsic neurones. 



The fiber tracts of two specimens of larval Amblystoma, 

 respectively 17 mm. (23 days after fertilization) and 38 mm. long, 

 prepared by the silver reduction inethod of Ramon y Cajal and 

 cut into transverse sections, were studied as completely as the 



