OPTICAL INSTRUMENTS STs) 
tion. It is unusual to think of a creature’s eye as one of 
its limbs, for only by a figure of speech do we describe a 
person as grasping the whole situation at a glance, Never- 
theless, there are very few inclined to dispute that the 
eyes of ‘the Podophthalma have really been developed upon 
appendages by nature equivalent to the rest of the series. 
Any one acquainted only with the extremely short-stalked 
eyes of some of the crabs might be excused for thinking 
this view extravagant, but its improbability is lessened 
when we observe the long-stalked eyes of the Angular 
Crab, Gonoplax rhomboides (Linn.), or those of the macruran 
Leucifer Reynaudit, Milne-Edwards, or those, again, of 
Hretmocaris longicaulis (see Plate XILI.), a shrimp in'which 
the eye is projected on a support actually longer than the 
animal. Moreover, the ocular appendage, besides being 
articulated to the head, is itself composed of two or three 
articulations. In the fast-running Ocypode cwrsor (Linn.), 
the peduncle is extended beyond the cornea of the eye, 
and terminates like an antenna in a pencil of long hairs. 
There is one instance on record in which the eye of a kind 
of lobster, Panulirus penicillatus (Olivier), has been observed 
to develop a jointed antenna-like lash, while the com- 
panion eye remained normal. ‘This evidence is parallel 
to that on which a botanist infers that the petals of a 
flower are by origin modified leaves when he sees them 
occasionally assuming the form of the unmodified leaf. 
2. The second segment carries the first pair of an- 
tennze, sometimes called the inner or upper, or, without 
epithet, the antennules. In the Malacostraca normally 
these appendages consist each of a three-jointed peduncle 
and two flagella or lashes, composed of many joints or 
few, the inner or secondary flagellum being not unfre- 
quently absent altogether or rudimentary. In some in- 
stances, and in the Amphipoda Caprellidea and in the 
Entomostracan Copepoda not as.an exception but as the 
rule, the first antenne are larger than the second, from 
which it results that the diminutive name antennules is 
rather convenient than appropriate. The superior size, 
however, is no indication of higher rank, but rather the 
