THE CLASS CRUSTACEA 313 



and temporary parasites. Of the latter, Argulus, a common 

 parasite of both sea and river fish, must be mentioned. In 

 Argulus the body is leaf-shaped and ill-segmented ; the 

 mouth-parts are suctorial, and in front of the mouth there is a 

 retractile hollow spine connected with large " poison-glands " ; 

 the maxillae are transformed into large adhesive suckers 

 which look like a pair of enormous eyes ; and a pair of eyes 

 is present. 



The species of the genus Cyclops (Fig. 134), some of which 

 are instrumental in carrying the guinea-worm, are typical 

 examples of free-living Copepods, and may be found in 

 abundance in any pond or ditch. They are minute, semi- 

 transparent, or — from the presence of food or fat — 



Fio. 134.— Female Cyclops, with Egg-sacks. 



greenish or reddish creatures, swimming with powerful jerks. 

 Examined under a lens, the body is seen to consist of an 

 anterior oval disk followed by a narrow tail, or abdomen, 

 which ends in a pair of long, feathered filaments. The front 

 of the disk is a true cephalothorax composed of 6 head- 

 segments and I thoracic segment, all united and carrying 

 diverse appendages ; the posterior half of the disk consists of 

 4 distinct thoracic segments, each bearing a pair of biramous, 

 jointed, feathery swimming legs. 



Of the appendages of the cephalothorax the most con- 

 spicuous are the first two pairs — the antennules and antennae 

 — the antennules, which are the chief organs of locomotion in 

 Cyclops, being of great length. Between the antennules, in 

 the mid-dorsal line, is a mass of black or red pigment — the 



