Sub-Class 1. Entomostraea. Order 6. Copepoda. 201 



The thorax consists of five segments, of which the foremost is 

 frequently united with the cephalothorax ; each segment, or only 

 the first four, bears a pair of swimming legs, consisting of 

 a short peduncle with two rami ; the outer ramus represents the 

 exopod; the inner, together with the peduncle, the endopod. The 

 abdomen is reduced and apodous, and is composed of the last five 

 segments of the body; at its posterior end there is a pair of unjointed 

 lamellate, or pointed, caudal appendages, between which the anus is 

 situated. The vascular system is poorly developed; the 

 heart usually wanting. Special respiratory apparatus 

 is also absent. The eggs are carried about by the female, 

 enclosed in one or two egg-sacs, which consist of a hardened glandular 

 secretion, and are attached to the base of the abdomen. The egg 

 hatches into an oval nauplius, with a nauplius-eye, and the 

 appendages (antennae, mandibles) characteristic of this developmental 

 stage, by means of which it swims actively about in the water. The 

 other limbs bud out gradually as the body increases in length. 



These Copepods are small aquatic animals, which are fresh- 

 water as well as marine, and are frequently found in immense 

 numbers ; the sea may be tinted red, over large tracts, by their 

 presence. The principal food of the great shoals of Herring consists, 

 at least in many places, of some species of this group, which 

 furnishes also a considerable contribution to the food of the Whale- 

 bone Whale. 



Species of the genus Cyclops, carrying two egg-sacs, are common in the 

 fresh, waters of England. 



The Parasitic Copepods comprise a multitude of different forms 

 living on (seldom in) different aquatic, usually marine, animals. 

 They are frequent upon Fish (especially on the skin and gills), also 

 on Worms, Molluscs, etc; they often attain a larger size than the 

 free-living forms (several c/m.). Some of them (Fig. 164, 1—2) e.g., 

 Fish-lice {Caligux), differ relatively little from the free-living forms. 

 The mandibles are modified as stabbing organs (stylets), which are 

 enclosed in a tube, the proboscis, formed by the concrescence of 

 the upper and under lips ; some of the limbs (second antennee, second 

 maxillae, maxillipeds) are modified to prehensile hooks (adhesive 

 organs) ; but in other respects those occurring, for instance, on the 

 skin of fish, are not strikingly different from the free-living forms,* 

 the sexes are not very dissimilar, and male as well as female, is 

 locomotor, not fixed to one spot on the host. In others the altera- 

 tion is greater, the adaptation to parasitic life closer ; this is specially 

 evident in the female. The modifications, which differ in extent in 



* It may be noted that the first antennsB, which, in free-living Copepods, are 

 generally very long, tend here to be rather short. The first maxilla is rudimentary, 

 the eye may or may not be present. Not infrequently {e.g. in Caligus), the body is 

 flattened, and accommodated to the surface of the host. 



