16 
PEOFESSOR H. N. MOSELEY". 
eyes occur in any numbers, thè eyes may be seen in all stages 
of formation. The eyes are formed in thè position whicli they 
always occupy wlien complete, uamely, witli thè stalk of thè 
pear-shaped pigmented capsule containing thè optic nerve 
turned towards thè margin of thè tegmentum adjoining thè 
girdle, and thè bulb of thè eye directed towards thè 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 thè pupil margin well defined. Next thè lens 
appears, and thè cornea and traces of thè nervous elements, and 
thè nerve capsule gradually becomes longer, and finally thè 
narrow canal into which it conti’acts is added. At each suc- 
cessive stage it appears like a segment of a complete eye, thè 
tail so to speak of which has been cut off transversely, less and 
less shortly. 
The megalsesthetes are similarly formed as thè tegraenta 
increase in growth at their free margins. By preparations so 
made as to show thè junction of thè margin of a tegmentum 
with thè girdle, thè raegalsesthetes may be seen in all stages of 
formation in a similar manner to thè eyes, There is no indi- 
cation of any enclosure of thè spines borne by thè girdle within 
thè substance of thè tegmentum in course of its formation, and 
there are no traces of any bodies resembling thè megalsesthetes 
or micresthetes in thè girdle tissues ; none such ever occur 
beyond thè actual margins of thè tegmenta. 
Presence or Absence of Eyes in Various Genera of 
Cliitonidse, differences in thè arrangement of 
thè Eyes when present, &c. 
In some genera of Chitonidse eyes are entirely absent. This 
is thè case with thè genus Chiton, which has, as shown by 
Marshall and van Bemmeleu, thè usuai megalopores and micro- 
pores, megalsesthetes and micrsesthetes, but in no species uf 
which I bave 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- 
