42 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



ences I have noted between the nervous systems of Tripedalia and 

 Charybdea. 



Nerve ring, radial ganglion and radial nerve all lie on the bell cavity 

 surface of the subumbrella. The way, now, in which the nerve ring 

 reaches the base of the stalk is simply by sending two roots through the 

 gelatine of the subumbrella to the conical base of the stalk. These roots 

 are seen in the diagram at rns. After passing through the gelatine the 

 roots come together on the inner side of the base that is, the side turned 

 toward the bell cavity and then pass downwards (nst) on the inner side 

 of the stalk of the club to the mass of nervous tissue at its end. 



This passage of nervous tissue through the gelatine in order to reach 

 the sensory club is a little hard to grasp at the first, and I have tried to 

 render it more intelligible by a couple of drawings of sections. Fig. 50 is 

 a transverse section through the upper part of the region of the sensory 

 niche, not quite horizontal (i. e. parallel with the bell margin), but slant- 

 ing so as to lie on the plane of the reference arrow x-y in Fig. 49. The 

 plane passes just through the top of the niche, and in two areas has cut 

 through the roof with its epithelium of ectoderm (ece, ecs) so that the 

 space of the sensory niche (sn) appears. The vascular lamella of the 

 sensory niche (vis) is shown, as in Figs. 13 and 14, running on each side 

 from the endoderm that lines the canal of the sensory club (enc) to the 

 endoderm of the adjacent stomach pocket (enp). By it the gelatine 

 of the exumbrella is separated from that of the subumbrella, and 

 one sees that it is only through the latter that the nerve has to pass in 

 order to reach the base of the sensory club. It is also seen that one part 

 of the roof of the niche which is cut through lies outside of the ring of 

 lamella and is therefore lined with ectoderm of the exumbrella (ece) 

 while the other lies within the ring and is lined with ectoderm of the 

 subumbrella (ecs). Owing to the slanting direction of the cut only the 

 root on one side is cut through. The other is indicated, however, on the 

 right side of the drawing. In this method of passage of nerve fibres, 

 together with the accompanying ganglion cells, directly through the gela- 

 tine to the stalk of the sensory club my work is only confirmation and 

 explanation of Glaus. 



Fig. 51 is a vertical section through the base of the stalk in the 

 plane of the reference arrow w-z in Fig. 49, and therefore passing 

 through one of the roots of the nerve of the stalk. Here again the 

 region is seen to, be cut off from the exumbrella by the vascular lamella of 

 the sensory niche (vis), and the nerve is seen passing through the gelatine 



