W. M. Coe — Anatomy of Cerehratulus lacteus. 503 



nuclei of cells which closely resemble those of the first type of nerve- 

 cells found in the dorsal brain-lobes. I believe these to be nuclei of 

 sensory cells, and the cephalic slits to be, for the most part, sensory 

 in their function. 



In the region of the dorsal commissure of the brain the lateral slits 

 become so deep (Plate X, figs. 2, 8, Is) that they reach internally 

 almost to the brain-lobes. After giving off the large canals (Fig. 3, cc) 

 to the side-organs the slits become suddenly shallow, and end a short 

 distance further back. The canal which thus arises from the poste- 

 rior end of each lateral slit passes backward in the ^gle between 

 the dorsal and ventral brain-lobes (fig. 3), to enter the side-organ at 

 its lower, outer and anterior border. Soon after its entrance into 

 the side-organ the canal bends sharply upwards to the dorsal border, 

 where it bends at a right angle and runs in this position nearly to the 

 posterior border. Here it again bends towards the inner side and 

 ends blindly among the masses of gland-cells which occupy the pos- 

 terior portions of the side-organs. 



The portion of the canal between the lateral slits and the side- 

 organs has a much wider lumen than that within the side-organs. 

 The lumen is lined with elongated columnar cells each bearing a 

 cluster of long, coarse cilia on the free surface, while the opposite end 

 is tapered to a slender, often branched, fibre. Among the bases of 

 the (Jells occur many sensory cells similar to those of the lateral slits. 

 At its entrance into the side-organ, the canal becomes decidedly 

 smaller and the nuclei are farther removed from the lumen. After the 

 canal (Plate XIV, figs. 1, 2, cc) has reached the upper and outer bor- 

 der of the side-organ, and throughout the rest of its course, there is 

 a marked difference in the character of the epithelium on one side of 

 the lumen. The columnar epithelial cells on the side of the canal 

 nearest the outer border of the side-organ are replaced by a smaller 

 number of very large and much modified cells. About six such cells 

 (fig. 2) are usually seen in a cross section of the canal, and to 

 these Dewoletzky (5) has given the name of '' lateral cells." Of these 

 six cells the two outer [k) are much longer than the others {h') and 

 from each a cluster of long cilia, adhering together to form a single 

 refractive column, projects a considerable distance into the lumen of 

 the canal.* Each of these cells may contain two or more nuclei in 

 its enlarged end which is farthest from the lumen. As Burger (2) 

 suggests, each of these " lateral border-cells " appears to be a consoli- 



* In Micrura afflnis these cilia are not consolidated into a single column, although 

 they are very long and are closely packed together. 



