44 Journal of Comparative Neurology. 



the epistriatum and probably the larger part of the fibers enter- 

 ing the epistriatum from the olfactory lobe come from the op- 

 posite side in this commissure. 



IV. Theoretical Considerations. 

 A. The Sensory Systems. 



Since a complete study of the cranial nerves has not been 

 attempted, there was included in the descriptive part only the 

 course of the nerve roots proximal to their ganglia. The identi- 

 fication of the sensory centers, however, has been based upon 

 the peripheral distribution of the nerves. The study of these 

 nerves has brought to light some important facts, and sufficient 

 description is given here to verify the account given of the roots 

 and to serve as a basis for theoretical conclusions. The study 

 was made upon haematoxylin and Golgi series. The distribu- 

 tion of the chief rami was determined by the distribution of 

 some branch or branches in each case. 



a. The sense organs' (Figs. 27, 28, 28 a). 



There are two sets of sense organs on the head and branch- 

 ial region of Lampetra. (The trunk region was not studied.) 

 One of these is innervated by lateral line nerves, the other prob- 

 alby by fasciculus communis components. The lateral line 

 organs are of the type called pit organs. The arrangement of 

 these is shown in Fig. 28, which represents the lateral and ven- 

 tral surfaces of the head, and the structure of one organ in 

 Fig. 28 a. There is an irregular and incomplete paired ventral 

 row extending through the branchial region and becoming reg- 

 ular and complete near the buccal cavity. In one specimen 

 these rows were made up of forty-one organs on one side and 

 fifty-four on the other. Continuing from the front end of this, 

 a row of about thirteen organs runs laterally and forward par- 

 allel with the border of the mouth. At the caudal end the 

 ventral rows bend laterally toward the last gill slit. Below and 

 in front of the first gill slit is a group (not a row) of from three 

 to six organs. Beginning at the ventral boundary of the cornea, 

 within the border of the eye, and running upward and forward 



