64 JOHNS HOPKINS UNIVERSITY MOEPHOLOGICAL 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 Glaus 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. Xayrnacana. 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. 



