6o4 Journal of Comparative Neurology and Psychology. 



anterior border. In fishes I have seen none of the large cells along 

 the course of this bundle caudal to the velum medullare anterius. 

 In Necturus the cells are found throughout the length of the 

 tectum, are most numerous in the posterior part and are very few 

 near the anterior border. Except near the anterior border, every 

 transverse section of the tectum shows from three to six of these 

 cells and one or two of the number are situated laterally, somewhere 

 within the medial one-half of the tectum. One cell was seen at the 

 lateral border of the tectum. In Cryptol^ranchus the arrangement is 

 similar, but the greater number of cells are in the anterior half of 



Fig. G. a, trausverse section of the uiesencephalon of the toad. A section 

 tlu'ougli the anterior part of the lateral cavities was drawn and the cells 

 inserted under the camera from several sections farther forward. The cells 

 near the middle lie in the section outlined, those at the sides mostly lie in 

 front of the lateral cavities. B, three sections through the posterior, middle 

 and anterior parts of the tectum of Scyllium. Only the outline of the aqueduct 

 is drawn and the cells in their proper position with reference to it. 



the tectum, while in the posterior half the cells are more strictly 

 grouped at the median line, i. e., in the roof plate. In the frog the 

 cells are fewer in number and, so far as I have seen, are placed far 

 laterally in the dome-shaped tectum. In the toad the cells are much 

 more numerous than in the frog. They are situated in the anterior 

 part of the tectum, there being two large groups in the anterior 

 bulging wall of the tectum connected by a large continuous collection 

 which extends across the median line (Fig. 6). The urodeles show 

 close similarity to the selachians ; the anura show great specializa- 

 tion in the arrangement of these cells. 



