COPEPODS 



343 



degenerate. The free-living Copepods form an important part of 



the food-supply of fishes. 



Cyclops, free and exceedingly prolific in fresh water. Its 

 appendages are : — antennules, antennae, mandibles, first 

 maxillae, second maxillae, four pairs of flattened biramous 

 thoracic legs united across the middle with those of the 

 opposite side, another rudimentary pair, and probably the 

 genital valve. Cetochilus, Calanus, free and abundant in 

 the sea. In Chondr acanthus, as in many other cases, the 



Fig. i88.— Crc/o/)<> type. 



lA., First antenna; HA., second antenna; OV., ovary; R.S. 

 receptaculum seminis ; OS., ovisac ; F., caudal fork. 



parasitic females carry the pigmy males attached to their 

 body. Caligus, a very common genus of "fish-lice." In 

 the carp-lic3 {Argulus) the mouth is a sucker with sharp 

 stilets and the second maxillaj form adhesive discs. 



Lerncea, Penella, etc. The adult females are parasitic, and 

 almost worm-like. The males and th= young are free. 

 Order 4. Cirripedia. — Barnacles and acorn-shells, and some allied 

 degenerate parasites. 



Marine Crustaceans, w^hich in adult life are fixed head down- 

 wards. The body is indistinctly segmented, and is enveloped 



