6 
PROFESSOR H. N. MOSELEY. 
vertently ignored thè clairas of these authors to priority in tliis 
matter. 1 am much indebted to Dr. Marshall for having 
kindly drawn my attention to thè two papers. My study of 
thè structure of thè shells in numerous genera of thè Chitonidse 
in connection with my investigation of thè structure of thè 
eyes has, however, I believe, thrown much new light on thè 
nature and homologies of thè papilliform organs. 
Methods. 
My observations bave been principally made on vertical and 
horizontal sections of decalcified shells. In my investigations 
on thè structure of coral, I bave had much experience in thè 
decalcification of tissues for thè purpose of histological exami- 
uation. I bave tried many methods of slow decalcification 
recommendedj with thè result of finding that for all purposes, 
including thè decalcification of thè shells of Mollusca, a com- 
paratively rapid decalcification with nitric acid yields thè best 
results. I place thè fragmeuts to be softened, which bave 
previously beeu hardened in strong alcohol^ in a vessel holding 
several ounces of distilled watei% and add concentrated nitric 
acid drop by drop till a brisk ebullition commences, making 
a three or four per cent, solution. If thè decalcification is not 
completed in twelve hours, I transfer thè object into fresh 
distilled water and add acid as before. I obtain better results 
by this method than any other. 
Structure of thè Shells and their Contained Soft 
Tissue Ramif ications. 
The tegraenta of thè shells of nearly allj if not all, Chito- 
nidse are perforated at thè. surface by circolar apertures or 
pores of two sizes, arranged in more or less definite patterns 
with regard to one another, and sometimes with regard to thè 
eyes also. As thè arrangement of these pores must in future 
become of systematic importance it is convenient to adopt 
some terms for them, and I shall cali them megalopores and 
micropores. The pores are constantly thus of two sizes, thè 
