38 
PROFESSOR H. N. MOSELEY. 
Literature of the Subject. 
It is remarkable that the eyes of the Chitonidae should have 
hitherto escaped notice. The main reason why they have done 
so is probably the fact that they do not occur, as far as I have 
been able to ascertain, on any common European representa- 
tives of the group such as have been ordinarily chosen for 
research by morphologists. Further, they are as a rule not 
easily seen in dried specimens of the shells, such as are mostly 
under observation in museums. It is not until these are 
wetted with spirit that the eyes become conspicuous. Again, 
Schizochiton, in which they are largest and most evident, is a 
rarity in museums. A molluscan shell is, moreover, almost 
the last place in which the naturalist would expect to find 
eyes, and the Chitonidae have hitherto in text-books always 
had the absence of eyes assigned to them as one of the charac- 
teristics of their group. 
Middendorf 1 named the two distinct layers, of which the 
shells of Chitonidae consist, the tegmentum and articulamentum; 
and Dr. W. B. Carpenter examined the shells of Chitons by 
means of sections, and observed the perforate structure of the 
tegmentum in Chiton, writing as follows : “ In Chiton the 
external layer, which seems to be of a delicate fibrous texture 
but which is of extreme density, is perforated by large canals 
which pass down obliquely into its substance, without pene- 
trating, however, as far as the middle layer. (Dr. Carpenter 
has kindly lent me his original sections of Chiton shells, and 
from what I now know I am able to recognise parts of pig- 
mented eye-capsules in one labelled Chiton spiniger .)” 2 The 
late Dr. Gray wrote, in his paper on the “Structure of Chitons 
“The greater number of species have a part of the valve which is 
not covered by the mantle, but exposed. This exposed part con- 
sists of a perfectly distinct external coat, peculiar, I believe, 
1 “ Beitrage zu einer Malacozoologia Rossica,” ‘Mem. de l’Acad. de St. 
Petersbourgh Sc. Nat./ Ser. iv, t. vi, 1849. 
2 ‘ Cyclopaedia of Anatomy and Physiology,’ article “ Shell,” p. 565, 
