ARTHROPODS. CLASS CRUSTACEA 109 
bottom. It is very cautious and cunning, capturing its 
prey by stealth, and with weapons which it knows how to 
conceal. Lying hidden in a bunch of seaweed, in a crevice 
among the rocks, or in its burrow in the mud, it waits until 
its victim is within reach of its claws, before striking the 
fatal blow. The senses of sight and hearing are probably 
far from acute, but it possesses a keen sense of touch and 
of smell, and probably also a sense of taste.” 
Although enclosed in a horny and often very thick and 
strong armor, the sense of touch is very keen in the 
Crustacea and in arthropods generally. On many of the 
more exposed portions delicate hairs or pits connected 
with the nervous system occur in great abundance. Some 
of these, usually on the antenne, undoubtedly serve in 
detecting odors, but the remainder are considered to be 
tactile. In the higher Crustacea, such as the crayfish, 
lobsters, and crabs, ears are usually found, consisting of 
sacs lined with similar delicate hairs, and containing sev- 
eral minute grains of sand, which in many cases make their 
way through the small external opening. Vibrations com- 
ing through the water gently shake the grains of sand, 
causing them to strike against the hairs which communi- 
cate with the nervous system—a very simple ear, yet suffi- 
cient for the needs of the animals. 
The eyes of the Crustacea and arthropods in general are 
either simple or compound. The simple and frequently 
single eyes usually consist of a relatively few cells embedded 
in a quantity of pigment and connected with the nervous 
system. It is doubtful whether they perceive objects as 
anything more than highly blurred images, and perhaps 
they merely recognize the difference between light and 
darkness. The compound eyes, on the other hand, are 
remarkably complex structures, often borne on the tops of 
movable stalks, as in the common crabs and crayfishes. 
Each consists of an external transparent cornea, divided 
into numerous minute hexagonal areas corresponding to as 
