152 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
no reason for believing that in this form there are mesenchymatous 
muscle fibers. 
(d) The inner layer of connective tissue, the fourth layer of 
the wall, is well developed throughout the whole extent of the 
alimentary tube in Caudina; it is everywhere the thickest of the 
layers. It closely resembles the connective tissue of the integu- 
ment, except that it is less compact. Bipolar or stellate cells, 
like those of the body-wall, are found at intervals, and the various 
sorts of wandering cells, to be described in connection with the 
internal epithelium, are abundant. In the small intestine great 
blood-spaces occur in this layer (Plate 5, fig. 54). 
I have found that in Cucumaria frondosa the stomach is entirely 
without an internal layer of connective tissue (Plate 5, fig. 53). 
This is in accord with the observation of Hamann, that in Cucumaria 
cucumis and C. Planci, this inner layer of connective tissue, every- 
where so well developed in Caudina, is lacking in the pharynx 
and insignificant in amount in the wall of the stomach, though 
reappearing in the small intestine. 
The absence of such a layer, which is everywhere the bearer of 
wandering cells connected with digestion, and in Caudina is the 
channel by which blood corpuscles come into connection with 
the internal epithelium, is readily explained. The thick lining of 
cuticula, the extremely muscular walls of the stomach of Cucumaria, 
as well as the absence of gland cells and amoebocytes, clearly 
indicate that the function of the stomach in Cucumaria is to 
triturate the food rather than to assist in its absorption. Hence 
the lack of the connective-tissue layer in this genus. 
(e) The inner epithelium is composed of columnar supporting 
cells interspersed with gland cells; between these are found wan- 
dering cells. 
a. The epithelium of the pharynx (Plate 5, fig. 51) consists 
of cylindrical cells — the deep ends of which are not well marked 
off from the connective-tissue layer —and long tubular gland cells, 
which are of two or three times the length of the supporting cells. 
A thin cuticula lines the pharynx. 
The deep ends of the gland cells are often enlarged by an 
oval swelling. An elongated, diffusely staining nucleus embedded 
in a small amount of protoplasm is found flattened against the 
