64 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 
The concretion filling the lithocyst has the shape of a hemipro- 
late spheroid cut in the plane of the axis of revolution. Whether 
it is of endo- or of ectodermal origin, I believe developmental studies 
only can determine. Tests made in the Chemical Laboratory show 
the presence of calcium sulphate with perhaps a very small trace of 
phosphate.* Nitric acid slowly dissolves these concretions, but I 
believe Claus was mistaken when he said that they dissolve with an 
evolution of gas. I watched them dissolve under the microscope, and 
never could see the least bit of gas formed. If Claus’s observation is 
correct, then the composition of the concretions of C. marsupialis is 
different from that of the concretions of C. Xaymacana. The concre- 
tions, further, were dissolved out of the material preserved in formaline 
and in osmic acid solutions. For dissolving them in situ I used either 
nitric or hydrochloric acid, or both. A slight husk remains after all 
the lime is dissolved. 
The Epithelium of the Clubs.—The epithelium is thickest on the 
dorsal side of a club. The thickening here, as in several other 
places, seems to be due to a crowding of the cells, in consequence of 
which the nuclei come to lie at different levels, but I believe that all 
the cells quite reach the surface. The cells with their nuclei nearest 
the surface are pyramidal in shape, with the bases of the pyramids 
toward the surface, while those cells whose nuclei lie deeper (where 
several layers of nuclei occur) may be spindle-shaped (Figs. 12, 23, 
24, 26). Centrad these cells are continued into a single process, which 
often seems to extend to the basement membrane (Figs. 7, 12, 13, 23, 
24). Where the epithelium covers the region of the concretion, the 
cells become flattened and with the long axis of their nuclei parallel 
with the surface of the club (Fig. 7). The same holds true for the 
corneal epithelium (Figs. 7, 13). 
It is a significant fact that in many places the nuclei form only 
a single layer, and in such places one cannot speak of spindle-shaped 
cells. I cannot find any evidence of sensory and supporting cells as 
Schewiakoff describes. The fact that spindle-shaped cells may exist 
is simply a physical consequence of their being closely crowded. 
Conant arrived at the same conclusion. 
But I have another and better reason for supposing the existence 
*Mr. J. C. Olsen, of the Chemical Laboratory, kindly made these tests for me. 
