u. 



SUCTORIAL CRUSTACEA; SIPHONOSTOMA. 277 



ters may be understood from those of the two genera Argulus 

 and Caligus, which will be briefly described, 

 The Argulus has its body covered with an 

 oval shield, which does not extend, however, 

 over the posterior part of the abdomen. 

 There are four pairs of legs, somewhat re- 

 sembling those of the Branchiopoda, and 

 2 adapted for swimming. The tail also is a 



FIG. coa-ARGULus FoLrA- kind f sw i mmeret . Qn each side of the 



CEUS. 1, the animal mag- 

 nified; 2, one of the large beak or proboscis, there is a large short 

 anterior sucking-feet ,3, i -i i . i i 



the siphon ; 4, natural cylindrical appendage, terminated by a cu- 

 len & th - rious sucking-disc ; and there is also a pair 



of larger jointed members, terminated by prehensile hooks. These 

 two pairs of organs, enabling the animal to attach itself firmly 

 to that on which it lives, are probably the representatives of the 

 feet-jaws. The eggs of the Argulus are deposited upon floating 

 bodies, like those of the Cyclops ; and the young, when they first 

 come forth, bear a strong resemblance to those of that genus. 

 Their swimming organs consist of the oar-like antennae and feet- 

 jaws ; the true swimming legs, and the suckers and hooks on the 

 feet-jaws of the adult, not making their appearance until after 

 several moultings. These Crustaceans may be regarded as in 

 several respects intermediate between those of the preceding 

 Order and the true Suctorial Crustacea ; for, even in the adult 

 state, they swim about actively in the water, and only adhere to 

 their victim when actually engaged in sucking. 



889. The Caligus (Fig. 609) is much more strange in its form. 

 Its body is composed of two principal portions ; the anterior one 

 covered by the oval, shield or carapace (Fig. 610, a) ; the poste- 

 rior, forming the termination of the thorax and the rudimentary 

 abdomen, is divided into rings. The first pair of antennae is re- 

 duced to the condition of small flattened plates, in some species 

 bearing a sucker. The antennae of the second pair (b) also are 

 short, and composed of only two joints. At c is seen a sucker, 

 formed by the labrum, and inclosing the mandibles. The maxillae 

 (d, e) are represented by two pairs of rudimentary appendages, 

 situated at the sides of the sucker, one of them terminated by 



VOL. II. X 



