786 



FRESH-WATER BIOLOGY 



8 (i) Head fused with first thoracic segment, but fusion indicated by 



distinct indentations on lateral margins; carapace half en- 

 tire length and violin-shaped 9 



9 (10) Second antennae as long as carapace. 



Ergasilus versicolor Wilson 191 1. 



Found upon species of catfish. 



Fig. 1240. Ergasilus versicolor. (After Wilson.) 



10 (9) Second antennae only one-half length of carapace. 



Ergasilus chautauquaensis Fellows 1887. 



Suborder Branchiura 



There is but one family in this suborder, — the Argulidae. They 

 are ectoparasites upon fish, and are commonly known as fish lice. 

 They have compound eyes, four or five pairs of swimming feet, and 

 the first maxillipedes are modified into a pair of sucking disks. In 

 connection with the mouth is a true stinging organ which pene- 

 trates the skin of the host. They are found most abundantly in 

 the branchial chamber of the host, but may attach themselves to 

 other parts of the body. It is a matter of interest in this connec- 

 tion, as has been noted by Wilson, that they attach themselves in 

 such a way as to place the long axis of the body parallel to that of 

 the host, so that they will be less Hkely to be brushed ofi in its move- 

 ments. To this end, too, the under side of the body of the Argulus 

 is armed with backward-pointing spines, which aid in keeping it 

 in place. Argulus is strictly dependent on the blood of its host 

 for food, but can and does frequently swim about freely. Inas- 

 much as the eggs are laid attached to stones and similar objects, it 

 must leave the host at the breeding season. They are not con- 



