PRESENCE OF EYES IN SHELLS OE CERTAIN CHITONlDiE. 21 
General Remarks. 
I regard thè megalaesthetes and micreesthetes as probably 
organs of touch which may to some extent take thè place of 
thè tentacles which are absent in thè Chitonidse. I base my 
conjecture as to their having a sensitive functiou on thè fact 
tliat thè megalaesthetes are in certain genera of thè Chitonidae 
converted into undoubted organs of special sense, viz. eyes. 
It is important that experiments should be made on living 
Chitons to determine whether thè aesthetes are protrusible and 
are used as organs of touch, and also as to thè sensitiveness to 
light of thè eyes. I bave searched in vain for any traces of 
eyes like those of thè Chitonidae in thè shells of Patella and 
allied genera. I am inclined to believe that thè megalaesthetes 
and micraesthetes are not, as van Bemmelen eoncludes, homo- 
logous with thè spines of thè girdle or rather with thè funicles 
by which these spines are supported.^ The structure of thè 
megalaesthetes seems to me to be quite peculiar and distinct. 
The funicles of thè girdle spines never give off a series of 
small offsets like thè micraesthetes. The eyes are obviously 
homologous with thè megalaesthetes, yet in none of thè 
Chitonidae is there a trace of an eye or part of an eye in thè 
girdle region beyond thè margin of thè tegmentum. In thè small 
plates of shell developed on thè girdle in thè Chitonidae and 
other genera, there are never any megalopores or microspores, 
or any traces of megalesthetes or micresthetes. 
The structure of thè girdle contrasts most markedly with 
that of thè tegmentum, and there is an absolutely sharp line 
of demarcation between thè two at thè place where they are 
in contact. This is well to be seen in Onithochiton. In thè 
shell are seen thè megalaesthetes and micraesthetes arranged 
with exact regularity and thè eyes extending up to thè very 
margin where some of both are seen, as yet only half formed, 
whilst in contact with these half-formed growths is thè 
marginai line of thè girdle devoid of micraesthetes and mega- 
1 Van Bemmelen, 1. c., p. 9é, 95. A. W. Hubrecht, “ Morphology of thè 
Ampliineura,” ‘ Quart. Journ. Micro. Sci.,’ voi. xxii, 1882, p. 214;. 
