28 



NATURAL HISTORY OF ARTHROPODS. 



Fig. 35. — Nogasus 

 latreillei. 



with blood. Indeed, if one may judge from specimens kept in aquaria, it seems to 

 prefer the free life except when hungry. Argulus (the type of the Family AEGULiDiB 

 through which the Siphonostomata are connected with the Phyllopoda and Ostracoda) 

 has a flat body, oval in outline, with a bilobed abdomen, four pairs of two-branched 

 swimming legs, besides the antennae and mouth-parts. On each side of the mouth is a 

 large round sucker, by whose aid they attach themselves to the skin and gills of the 

 fishes on which they prey. They possess pointed mandibles, through 

 which they obtain the blood, and have, besides, a median needle-shaped 

 organ, probably connected with poison-glands, by which they may 

 pierce the skin of the host, and by the poison stimu- 

 late the flow of blood. There are two large eyes, and 

 the antennae are present. So highly organized an 

 animal — one so well fitted for an independent life 

 is hardly a true parasite. It is parasitic at times, 

 and when its sacculated, intestine is filled with blood 

 may or may not return to a free life. 



A second group of the Siphonostomata contains 

 the Caligid^. Here belong very numerous species of 

 fish-lice. These have still well-developed appendages, 

 but they are fitted for clinging to the host rather than 

 for swimming, and the forms of Caligus and allied 

 genera are sessile though capable of locomotion. 

 They have a sucking proboscis, which encloses the 

 mandibles. They live, mainly attached to the gills of various fishes, 

 on whose blood they live. They may often be found by separating the lamellae of 

 the gills. Here also belong the genera Pandarus and " iVb^asws," which we illus- 

 trate. The latter genus is very doubtful, the individuals being in all probability the 

 males of forms assigned to other genera. Both forms are parasitic on 

 fishes, the individuals figured being attached to Atwood's shark ( Car- 

 char odon atwoodi). 



In Dichelesthium and its allies, which form the family Dicheles- 

 THiiD^, degradation is carried a step further. The limbs are often 

 aborted so that locomotion is possible only by bending the body. Their 

 habits are much the same as those of the preceding gi-oup. 



In the family Leen^eid^ {Lernea, Lernoeonema, jPenella, IToemob- 

 aphes, and related forms) the effects of parasitism are carried much fur- 

 ther. The segmentation of the body is scarcely marked, 

 the limbs are stumpy projections, and the head is armed 

 with projections which aid in fixing the animal to its host. 

 They are rather worm-like than crustacean in appearance. 

 They live attached to the skin or gills of fishes of all kinds, 

 or in some of their species buried in the muscles of their 

 victim. The males are not parasitic, and are of the usual 

 crustacean form, and the young are Cyclops-like. The 

 distorted form of the adult female is reached after the 

 parasitic life is begun. 



In the Leen^opodid^, the last family we have to 



Fig. Si.— Panda- 

 rus. 



Fig. 36.— IIcBmo- 

 baphes. 



mention, embracing JLernceopoda, Diocus, and AnchoreUa, mlema raduua. 



