370 THE INVERTEBRATA 



and passed towards the mouth by the endites and endopodites of the 

 maxillules, assisted by the gnathobase of the maxillae. The first trunk 

 limb is used in crawling, and the second in cleaning. Cypris lacks the 

 compound eyes and the heart, which are found in some other members 

 of the class — for instance in the marine Cypridina, which is also 

 characterized by a large antennal exopodite, turned outwards in a 

 notch of the shell for rowing. 



an.— 



an: 



jTh.Q 



ram. 



Fig. 248. Lateral view of Cypris. After Zenker, an/ antennules; an." an- 

 tennae; md. mandibles; mx.' ist maxillae; mx." 2nd maxillae; Th.i, Th.2, 

 thoracic limbs ; ram. ramus of caudal fork ; e. eye. 



Class COPEPODA 



Free or parasitic Crustacea, without compound eyes or carapace; 

 with biramous or uniramous palp, or with none, on the mandible; 

 and typically with six pairs of trunk limbs, of which the first is always 

 and the sixth often uniramous, the rest biramous, and none are 

 situated behind the genital aperture (i.e. on the abdomen). 



The form of the body varies greatly in the members of this class, 

 from the pear-shaped or club-shaped free-swimming genera to the 

 distorted, unsegmented, and sometimes even limbless adults of some 

 of the parasites. In all cases in which the segmentation is complete 

 the number of somites is the same — sixteen, including a preantennu- 

 lary somite but not the telson — throughout the group, but the actual 

 tagmata, which do not conform to the limits of the head, thorax, and 

 abdomen, are not uniform in all members of the class. 



We shall take as an example of the group the little freshwater 

 crustacean Cyclops (Fig. 249) which, though it is not one of the most 

 primitive members of the Copepoda, is well segmented and can be 

 obtained everywhere in ponds and ditches. The shape of this animal 

 is that of a slender pear with a stalk. The front part of the pear is 

 unsegmented; this is a compound head or "cephalothorax", com- 

 posed of the true head and the first two thoracic somites : beneath, in 

 front, it bears a blunt projection, the rostrum. The rest of the broad 



