AMERICA N PA RASITIC ARG ULID.E— WILSON. 653 



always practically assured of a suitable host and assisted in any effort 

 it may make toward concentration. These facts render it certain 

 that if the breeding* of Argruli is once started in such places it will 

 rapidl}^ assume dangerous proportions unless checked at the very 

 beg'inning. 



The introduction, repeated if necessary, of some of the small iish 

 that naturally prey upon crustacean larvie, could do no possible injury, 

 and in the light of this investigation bids fair to prove an etfective 

 remed}', 



SUMMARY. 



1. The Argulidie are external parasites, usually contined to the 

 branchial cavity of their host. 



2. They cling ])v means of the anterior maxillipeds, which are mod- 

 itied into sucking disks for this purpose, and ])y a walking motion of 

 these same disks they scuttle about over the lish's skin so long as it 

 remains moist. They can not fasten to a dry surface. 



8. They always take a position with the long axis of their bodies par- 

 allel to that of their host and with their heads in the same direction. 

 They are kept from slipping' backward, as the fish darts through the 

 water, by the sucking disks just mentioned, b}- large curved hooks on 

 the bases of the anterior antenna?, by stout spines on the bases of l^oth 

 pairs of antenna and often between the bases of both pairs of maxilli- 

 peds, by rough plates on the bases of the posterior maxillipeds, usually 

 with three stout spines along- their posterior border, and by short 

 triangular spines all over the ventral surface of the carapace, but 

 especiall}' numei-ous along the anterior margin. All these spines 

 point diagonally downward and backward, and at the slighest backward 

 movement they catch firmly in the fish's skin, and, of course, the greater 

 the pressure the more firmly the}' hold. 



•i. The Argulidie retain their locomotor ability to a greater degree 

 than any of the other parasitic copepods. Both males and females 

 swim with an easy, gliding motion, free from jerkiness. The four 

 pairs of legs serve as locomotor organs, and steering is accomplished 

 chiefly b}^ a flexion of the thorax on the head carapace, though the 

 abdomen assists somewhat. The length of the plumose sette on the 

 legs seems to determine the rapidity of movement. 



5. In consequence of its freedom of motion an Argulus is not con- 

 fined to one species of fish, but can change its host at pleasure. Hence 

 the host list is quite large for all the well-known species and will prob- 

 abl}" increase with further observation. 



6. Both sexes, but especialh' the males, leave their host at the breed- 

 ing season, since the eggs are not carried about, but are deposited on 

 some favorable surface, usually at the bottom. Hence at least three 

 times a year an infested fish has a chance to get rid of these parasites. 



