F. S. CONANT ON THE CUBOMEDUS^E. -41 



they cannot be so numerous as has been supposed. The position of the 

 nuclei shows that. 



The epithelium of the nerve is said by Glaus to be ciliated. It has 

 been suggested by Schewiakoff that probably in such cases the sensory 

 cells bear one long cilium, while the supporting cells have many smaller 

 cilia. Unfortunately, I made no observations upon the ciliation of the 

 nervous structures of the living animal, and the traces of cilia that are 

 shown in preparations of preserved material are a poor basis to speculate 

 much on. Claus considers the sensory cells of the epithelium of the 

 nerve a special seat of tactile sensation. 



The way in which the nerve reaches the sensory clubs is interesting. 

 Under the topic of the vascular lamella? it was explained that the sensory 

 clubs and the bottom of the sensory niche from which they spring are 

 parts of the subumbrella. Fig. 37 reminds at a glance better than any 

 other one drawing how the bottom or inner wall of the niche is com- 

 pletely cut off from the exumbrella by vascular lamellae above and below 

 the stalk of the club. From this figure, now, it will readily be under- 

 stood that the nerve in order to pass to the base of the stalk has simply 

 to traverse the gelatine of the subumbrella. This fact, which seems sur- 

 prising enough at first sight in view of the position of the clubs on the 

 external surface of the umbrella, was correctly pointed out and explained 

 by Claus, but one or two figures will serve perhaps to give a clearer 

 idea of it. 



Fig. 49 is a diagram of the nervous structures in the region of the 

 sensory niche, as they would be seen on the surface of the subumbrella 

 turned toward the bell cavity. The outline of the sensory niche as it is 

 seen through the tissue of the animal is represented by the line osn. 

 The sensory club (scZ), and its stalk with a conical basal portion are given 

 by the lightly dotted outline and are also imagined as seen through the 

 animal. The nerve (n), being on the surface of the subumbrella, is shown 

 as a heavy line describing an arch over the outline of the niche. In the 

 middle point of the arch is a slight thickening of the nervous tissue (>v/) 

 which shows in section a large increase in the number of ganglion cells, 

 and is the radial ganglion of Claus. The same is seen, exaggerated in 

 size, in Fig. 12. From it there extends upward a slender strand of 

 nervous tissue (rn), the radial nerve of Claus. In Charybdea this can 

 be traced but a very short distance. In Tripedalia it is much more 

 distinct and traceable for a longer distance, and I might say in passing 

 that this and the sensory organs in the proboscis are the only differ- 

 6 



