Constitution of some Appendages of the Mollusca. 777 
_ In various papers on the Mollusca, in which the dentition has 
been discussed, I have (and doubtless others have) called atten- 
Ša incidentally to the chitinous nature of the teeth of mollusks, 
méalso to the fact that those groups, believed to be of very 
ascent lineage, and to have been less altered from their early 
Matus than many others, have the teeth composed of chitinous 
Pts cemented together and to the radula with a horny cement 
which dissolves in boiling liquor potassa. This is the case in 
Docoglossa and Chitons. In these the base of the radula 
aad the above mentioned cement are probably of a truly horny 
stitution. In the Pulmonata the radula and teeth are of a 
higher character, and apparently purely chitinous, though in but 
of the groups has the jaw attained this constitution. 
itis well known that in some of the most highly organized 
‘B*ropods, such as Conus, the teeth are specialized, few in num- 
ber, in some cases tubular, barbed and furnished with a true poison 
| and and duct, by which a very severe injury can be inflicted on 
* assailant, even a conchologist. The secretion of sulphuric 
mal by the genus Dolium is doubtless connected with its habit 
its teeth and radular apparatus, and the secretion of such 
‘Stength that it must form a very efficient solvent, and greatly 
“sten the desired result. It may also be used as a poison against 
so-bodied adversary, but this is not definitely known. The 
Satement of Professor Lankester that the jaws of mollusks are 
"sually calcified,” is entirely erroneous. That some of them 
have a calcareous coating or reinforcement is possible, 
no such case is known to me, but at any rate it must be 
Very exceptional occurrence. 
Dr. 0. Loew, well known for his chemical investigations, when 
“acted with the Wheeler survey was kind enough to under- 
at my suggestion, some qualitative analyses of organic pro- 
for which I furnished the materials, about 1875- 
ig ine the nature of the molluscan jaw a number of the 
eh i cephalopods (probably Loligo) were examined. The 
Sak homy matter yielded very slowly to prolonged boiling in 
d liquor potassæ, but after this result a pellucid portion 
aned retaining the exact form of the jaw and about one-third 
total volume. This was boiled in strong acids and alka- — 
a long time without yielding or being visibly affected. 
