206 MANUAL OF ZOOLOGY. 



is termed the " epipodite." The succeeding segment supports 

 a pair of limbs similar to the last in all respects, except that 

 its extremities, instead of being simply pointed, are converted 

 into nipping claws, or "chelae." The next segment of the 

 thorax carries a pair of chelate limbs, just like the preceding, 

 and the next is furnished with . appendages, which are essen- 

 tially the same in structure, but are much larger, constituting 

 the great claws. The next two segments of the thorax, and 

 the segment in front of these (by some looked upon as belong- 

 ing to the head, by others as referable tO the thorax), bear 

 each a pair of modified limbs, which are termed *' maxillipedes," 

 or " foot-jaws." These are simply limbs with the ordinary 

 structure of protopodite, exopodite, endopodite, and epipodite, 

 but modified to serve as instruments of mastication, the hind- 

 most pair being less altered than the two anterior pairs (fig. 62, 

 3). The next two somites carry appendages, which are in the 

 form of jaws, and are termed respectively the first and second 

 pairs of " maxillae." Each consists of the parts aforementioned, 

 but the epipodite of the first pair of maxillae is rudimentary, 

 whilst that of the second pair is large, and is shaped like a 

 spoon. It is 'termed the " scaphognathite," and its function is 

 to cause a current of water to traverse the gill-chamber by con- 

 stantly baling water out of it. The next segment carries the 

 biting jaws, or " mandibles ; " each of which consists of a large 

 protopodite, and a small endopodite, which is termed the 

 " palp," whilst the exopodite is undeveloped. The aperture 

 of the mouth is situated between the bases of the mandibles, 

 bounded behind by a forked process, called the " labium," or 

 "metastoma," and in front by a single plate, called the "la- 

 brum" (upper lip). The next segment bears the long antennae, 

 or feelers (fig. 74, ga), each consisting of a short protopodite, 

 and a long, jointed, and segmented endopodite, with a very 

 fudimentary exopodite. In front of the great antennae are the 

 next pair of appendages, termed the " antennules," or smaller 

 antennae (fig. 74, a), each composed of a protopodite, and a 

 segmented endopodite and exopodite, which are nearly of equal 

 size. Finally, attached to the first segment of the head are the 

 eyes, each of which is borne upon an eye-stalk formed by the 

 protopodite. The gill-chamber is formed by a great prolonga- 

 tion downwards of the pleura of the thoracic segments, and 

 the gills are attached to the bases of the legs. 



As regards the digestive system of the Crustacea, the ali- 

 mentary canal is, with few exceptions, continued straight from 

 the mouth to the aperture of the anu^;. There are no salivary 

 glands, but a large and well-developed liver is usually present. 



