50 
PROFESSOR H. N. MOSELEY. 
eyes occur in any numbers, the eyes may be seen in all stages 
of formation. The eyes are formed in the position which they 
always occupy when complete, namely, with the stalk of the 
pear-shaped pigmented capsule containing the optic nerve 
turned towards the margin of the tegmentum adjoining the 
girdle, and the bulb of the eye directed towards the shell apex. 
The first trace of a developing eye is a semilunar fold of pig- 
mented eye-capsule. This increases till it becomes horse-shoe 
shape with the pupil margin well defined. Next the lens 
appears, and the cornea and traces of the nervous elements, and 
the nerve capsule gradually becomes longer, and finally the 
narrow canal into which it contracts is added. At each suc- 
cessive stage it appears like a segment of a complete eye, the 
tail so to speak of which has been cut off transversely, less and 
less shortly. 
The megalsesthetes are similarly formed as the tegmenta 
increase in growth at their free margins. By preparations so 
made as to show the junction of the margin of a tegmentum 
with the girdle, the megalsesthetes may be seen in all stages of 
formation in a similar manner to the eyes. There is no indi- 
cation of any enclosure of the spines borne by the girdle within 
the substance of the tegmentum in course of its formation, and 
there are no traces of any bodies resembling the megalsesthetes 
or micresthetes in the girdle tissues ; none such ever occur 
beyond the actual margins of the tegmenta. 
Presence or Absence of Eyes in Various Genera of 
Chitonidse, differences in the arrangement of 
the Eyes when present, &c. 
In some genera of Chitonidse eyes are entirely absent. This 
is the case with the genus Chiton, which has, as shown by 
Marshall and van Bemmelen, the usual megalopores and micro- 
pores, megalsesthetes and micrsesthetes, but in no species of 
which I have been able to detect any trace of eyes. Van 
Bemmelen investigated Chiton marginatus, and I especi- 
ally by decalcification only C. magnificus and C. marmo- 
