40 
PROFESSOR H. N. MOSELEY. 
vertently ignored the claims of these authors to priority in this 
matter. 3 am much indebted to Dr. Marshall for having 
kindly drawn my attention to the two papers. My study of 
the structure of the shells in numerous genera of the Chitonidse 
in connection with my investigation of the structure of the 
eyes has, however, I believe, thrown much new light on the 
nature and homologies of the papilliform organs. 
Methods. 
My observations have been principally made on vertical and 
horizontal sections of decalcified shells. In my investigations 
on the structure of coral, I have had much experience in the 
decalcification of tissues for the purpose of histological exami- 
nation. I have tried many methods of slow decalcification 
recommended, with the result of finding that for all purposes, 
including the decalcification of the shells of Mollusca, a com- 
paratively rapid decalcification with nitric acid yields the best 
results. I place the fragments to be softened, which have 
previously been hardened in strong alcohol, in a vessel holding 
several ounces of distilled water, and add concentrated nitric 
acid drop by drop till a brisk ebullition commences, making 
a three or four per cent, solution. If the decalcification is not 
completed in twelve hours, I transfer the object into fresh 
distilled water and add acid as before. I obtain better results 
by this method than any other. 
Structure of the Shells and their Contained Soft 
Tissue Ramifications. 
The tegmenta of the shells of nearly all, if not all, Chito- 
nidse are perforated at the surface by circular apertures or 
pores of two sizes, arranged in more or less definite patterns 
with regard to one another, and sometimes with regard to the 
eyes also. As the arrangement of these pores must in future 
become of systematic importance it is convenient to adopt 
some terms for them, and I shall call them megalopores and 
micropores. The pores are constantly thus of two sizes, the 
