GEROULD: CAUDINA. 131 
The cylindrical or conical bundles of cells which are found upon 
the oral side of the axial pair of tentacular processes (Plate 2, fig. 16) 
consist mostly of sensory cells; each bundle is connected with a strand 
of nerve fibers which arises from the tentacular nerve and among 
which are interspersed ganglion cells. These groups of cells resem- 
ble in some respects the sensory buds upon the tentacles of Synapta, 
but the epithelium surrounding the group of nerve cells in Caudina 
is not modified to form a protecting envelope, nor have 1 found a 
ciliated depression upon the surface of the group such as Hamann 
has described in Synapta. Iregard these groups of cells as: simple 
form of sensory bud. 
2. CONNECTIVE-TISSUE LAYER. 
The layer of connective tissue is thinnest in the anterior part of 
the body; immediately behind the tentacles it measures only 170 a 
in thickness, whereas only a short distance posterior to this, viz., 
opposite the posterlor extremity of the radial calcareous plates, it is 
290 y thick. In the middle of the body it may attain a thickness of 
350-430 u, while in the tail region it is slightly thinner. 
As in other holothurians, it is composed of a transparent homo- 
geneous matrix in which lie numerous fibers, among which are 
interspersed bipolar or stellate cells, the longest diameter of which in 
sections may be 15-16 w; each of these encloses an oval nucleus of 
perhaps 3 x 7 (Plate 1, fig. 2). Fibers arise from the cells just 
mentioned; the superabundance of fibers and scarcity of cells lead 
one to think it improbable that in Caudina the fibers are all 
prolongations of cells, though it is the opinion of Hamann that such 
is the case in certain holothurians, 
In the superficial portion of the layer of connective tissue (Fig. 
2) immediately beneath the epithelium are located the calcareous 
bodies, This is the couche aréolare of Jourdan and Hérouard. 
The connective-tissue fibers which entwine themselves around 
the caleareous bodies run in all direetions, but in the thiek deeper 
portion of the connective-tissue layer they run in general parallel 
to the surface of the body. 
In the connective-tissue layer and among the external epithelial 
cells are frequently found wandering cells (Plate 1, fig. 2, ep. sph.), 
called by Durham (92) spheruliferous corpuscles, the Plasma- 
