PRESENCE OF EYES IN SHELLS OF CERTAIN CHITONIDJl. 55 
General Remarks. 
I regard the megalaesthetes and micraesthetes as probably 
organs of touch which may to some extent take the place of 
the tentacles which are absent in the Chitonidae. I base my 
conjecture as to their having a sensitive function on the fact 
that the megalaesthetes are in certain genera of the Chitonidae 
converted into undoubted organs of special sense, viz. eyes. 
It is important that experiments should be made on living 
Chitons to determine whether the aesthetes are protrusible and 
are used as organs of touch, and also as to the sensitiveness to 
light of the eyes. I have searched in vain for any traces of 
eyes like those of the Chitonidae in the shells of Patella and 
allied genera. I am inclined to believe that the megalaesthetes 
and micraesthetes are not, as van Bemmelen concludes, homo- 
logous with the spines of the girdle or rather with the funicles 
by which these spines are supported . 1 The structure of the 
megalaesthetes seems to me to be quite peculiar and distinct. 
The funicles of the girdle spines never give off a series of 
small offsets like the micraesthetes. The eyes are obviously 
homologous with the megalaesthetes, yet in none of the 
Chitonidae is there a trace of an eye or part of an eye in the 
girdle region beyond the margin of the tegmentum. In the small 
plates of shell developed on the girdle in the Chitonidae and 
other genera, there are never any megalopores or microspores, 
or any traces of megalesthetes or micresthetes. 
The structure of the girdle contrasts most markedly with 
that of the tegmentum, and there is an absolutely sharp line 
of demarcation between the two at the place where they are 
in contact. This is well to be seen in Onithochiton. In the 
shell are seen the megalaesthetes and micraesthetes arranged 
with exact regularity and the eyes extending up to the very 
margin where some of both are seen, as yet only half formed, 
whilst in contact with these half-formed growths is the 
marginal line of the girdle devoid of micraesthetes and mega- 
1 Van Bemmelen, 1. c., p. 91, 95. A. W. Hubrecht, “ Morphology of the 
Amphineura,” ‘ Quart. Journ. Micro. Sci.,’ vol. xxii, 1882, p. 214. 
