F. S. CONANT ON THE CUBOMEDUS.K 33 



bend of the loop, so that in part of its course the lamella is cut almost 

 horizontally, i. e. in its own plane. Fig. 43 finally shows the lamella as 

 it appears below the level of the connecting canal, cut twice, each portion 

 joining endoderm of marginal pocket with ectoderm of surface. It tl\us 

 bears exactly the same relations that it had when we first met it in Fig. 

 38 (vim), except that here in Fig. 43 one finds that a cross-section cuts it at 

 right angles instead of a vertical as in Fig. 38, as a result of its being 

 pushed upwards from its former position on the margin by the insertion 

 of the pedalium above the margin. 



The vascular lamella of the sensory niche has already been alluded to 

 as part of the marginal system, and brief reference has been made to it 

 in the section on the sensory clubs. Like the rest of the marginal 

 lamella, it connects endoderm with ectoderm. The line that its fusion 

 with the ectoderm traces on the surface frames in a shield-shaped area 

 at the bottom of the sensory niche, which is seen in the drawing of the 

 outlines of the niche, Fig. 44 (vis). This lamella was observed by Claus, 

 and was figured by him both in surface view and in cross-section 

 through the niche. Apparently, however, he omitted vertical sections 

 through the niche, so that he supposed that the outline traced by the 

 lamella was not continuous above, i. e. over the stalk of the sensory club 

 (78, Fig. 41 ; text, p. 28). That the outline is closed above, though 

 masked in surface view by the roof of the sensory niche, is seen at once 

 in vertical sections, such as Figs. 37 and 38, one of which is directly 

 through the perradius, the other a little to one side. Both show the vas- 

 cular lamella of the sensory niche (vis) intersected twice, above and below 

 the sensory club, and completely cutting off the exumbrella from any 

 share in the bottom (or inner wall) of the sensory niche. Fig. 39, which 

 is a cross-section through the upper part of the niche, and is essentially 

 like the similar figure of Claus, shows in like manner that the bottom of 

 the sensory niche belongs to the subumbrella. H. V. Wilson was the 

 first to point out, in his unpublished notes, that the lamella of the niche 

 is complete all round. 



In the adult structure of Charybdea and Tripedalia the lamella of 

 the niche is connected with that of the margin by a vertical strip of 

 endodermal fusion that does not come to the surface like the rest of the 

 marginal system, but remains just internal to the gelatine of the exum- 

 brella, connecting the two adjacent marginal pockets. In the cross- 

 sections of Charybdea it is seen in Fig. 16 (vie) ; in those of Tripedalia it 

 is seen in Figs. 28 and 29. In vertical section it is found in Figs. 4, 19 

 5 



