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 slanting 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 (_vls_) 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 gelatine to the stalk of the sensory club my work is only confirmation and explanation of Claus.
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 (_vls_), and the nerve is seen passing through the gelatine of the subumbrella from the surface of the bell cavity (_sc_) to the base of the stalk hanging in the sensory niche (_sn_). One of the ganglion cells (_gc_) that accompany the nerve is seen to have two nuclei, a not infrequent occurrence which has been pointed out by others.