(b) The plain subectodermal _muscle-fibers_ are of interest. In Charybdea they lie wholly enclosed within canals of the supporting lamella (Fig. 32, upper part). They run longitudinally, and near the base of each tentacle pass out of their canals and become strictly subectodermal (Figs. 31, 32). This is for Charybdea. In Tripedalia they rarely come to lie in closed canals as in Charybdea. These facts show beyond doubt that these muscles are developed from the ectoderm. Claus has suggested their ectodermal origin, but did not demonstrate it. He also suggested that they become inclosed in canals by the supporting lamella pushing up around them and finally fusing above them. This, I believe, is demonstrated by the conditions in Tripedalia (Fig. 29). Here the canals usually remain open, but occasionally, as in the left-hand canal, one may become completely inclosed. This condition of things suggests the intra-lamellar muscles found in actiniarians. The nuclei found in the canals with the muscle-fibers probably belong to the cells from which the muscles become differentiated. Claus figures these muscle-fibers and nuclei, and it may be added that the supporting lamella he figures, for C. marsupialis, is much thicker than I have figured it for C. Xaymacana and Tripedalia cystophora. The number of muscle-canals also is greater and occupies a much greater depth of the thickness of the lamella. Since Claus gives a figure of a transverse section showing the muscles in their enclosed canals, I have not deemed it necessary to duplicate his figure. In the transition from a tentacle to a pedalium, the muscles are most strongly developed toward and at the edges of the pedalium. This is true for the pedalia in general, and accounts for the readiness with which they can be bent inwards, as noted in the physiological part of this paper. (c) I have found a single _ganglion-cell_ among the cells of the ectoderm of the tentacles. This showed so plainly that I have figured it (Fig. 28). Other ganglion-cells no doubt exist, but could probably not be distinguished from other cells. In its position in Fig. 28 it appears to be associated with the nettle-cell shown just above it. Its position is very much the same as that figured by Lendenfeld (25a). _The Endoderm._--The cells of the endoderm of a tentacle are long and quite slender (Fig. 31). At their bases they are vacuolated quite like the cells of the ampulla and the canal of the sensory clubs. They contain a well-formed nucleus with a nucleolus. In their distal half small light bodies with a dark center are very evident. These bodies are evidently a secretion.