168 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



frequently as much as 100 micra. The nucleus is always eccentric in its 

 position, sometimes so much so that it lies in a slight protuberance 

 from the body of the cell, as was noted by Houser (:01, p- 130). As in 

 Amia^ it is always located at the side of the cell opposite to that from 

 whicli the axon arises (Plate 3, Figs. 18-20). For instance, in the mid- 

 dle cells of the series, where the tapering process passes oft" dorsally, the 

 nucleus always lies at the ventral side of the cell close to the third ven- 

 tricle (Figs. 18-21). Occasionally a cell in this region sends its axon 

 directly ceghalad, in which case the nucleus is found at the posterior 

 end of the cell (Fig. 21). Again, near the posterior commissure, where 

 the axon may pass directly ventrad, the nucleus is eccentric and dorsal. 

 This, it seems to me, precludes the possibility that gravity plays any 

 part in determining the position of the nucleus, and forcibly suggests a 

 definite law in the relation of these parts, at least for these cells. 



The cytoplasm appears minutely granular under the highest powers, 

 due, as suggested by Houser, to the numerous small Nissl's granules. 

 The centre of the cell is, however, freer from these than the periphery, 

 where the granules are larger and more numerous (Fig. 19). 



As already implied, the cells are usually multipolar, giving oflF, in 

 addition to some finer dendrites, three principal processes (Plate 3, Figs. 

 19, 20). Frequently, however, the cells are bipolar, or even unipolar in 

 appearance (Figs. 18, 21). In the pyriform unipolar cells the single 

 process divides in T-form to give rise to the axon and cerebellar neurite. 

 The shortest of these three processes passes more or less directly laterad 

 and doi-sad with the fibres of the dorsal decussation (Figs. 18, ax', and 

 20) toward the ectal region of the tectum opticum, and is lost in the 

 stratum medullare profundum, where it comes directly in contact with 

 the endings of the proximally running fibi'es of the optic nerve. It is by 

 this process that the cell is put in direct connection with the outer 

 world through the retina. 



A second and much larger process forms, with others, the tractus 

 tecto-cerebellaris (Fig. 18, ax"). Usually this comes ofi" from the cell 

 separately, but it may arise by the division of the single process. In 

 the polygonal or elongated cells in the posterior portion of the tectum 

 it passes off" directly from the caudal end of the cell (Fig. 18). In the 

 anterior cells it more frequently arises by division. Whatever its man- 

 ner of origin, it takes a course laterad and dorsad from the cell, and 

 turning caudad joins with other similar fibres to form one of two fibre- 

 tracts on either side of the median plane (Plate 2, Fig. 12, trt. tct. cbl.) 

 which run caudad into the cerebellum (Plate 3, Fig. 15). These neu- 



