PARASITES AND MESSMATES 225 



species of the family Caligidae, 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, FlG - 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 



