PARASITES AND MESSMATES 225 



species of the family Caligidse, many of which, 

 belonging to the genera Caligus (Fig. 72), Lepe- 

 ophthirus, etc., are found on marine fishes on our 

 own coasts. In these the body is broad and flat, 

 but in many of them the resemblance, even in 

 general form, . to the free- 

 living Copepoda is easily 

 traceable. The maxillipeds 

 form powerful hooked claws, 

 by means of which the ani- 

 mals cling to the skin of the 

 fish they infest, and in Caligus 

 the basal segments of the 

 antennules have a pair of 

 suckers which aid in ad- 

 hesion. The mouth parts 

 are adapted for piercing, and 

 are enclosed in a suctorial 

 proboscis. 



When the young Caligid, 

 after passing through the 

 free-swimming larval stages, FIG- 72 A FISH-LOUSE 



(Caligus rapax), FEMALE. 



first becomes attached to a x 5. (After Wilson.) 

 fish, it adheres by means of a 



thread-like process issuing from the front of the head, 

 and formed by the secretion of a gland. At this 

 stage, formerly described as an independent species 

 under the generic name of Chalimus, the parasite is 

 unable to detach itself from its host ; but later, in 

 15 



