AMERICAN PARASITIC ARGULIDjE— WILSON. 



681 



huge chitinous hook and in some species {latlcauda) does not reach 

 beyond the hitter. 



The hirval development shows that this prehension which so pre- 

 dominates in the adult is really acquired and that the antennas are 

 originally tactile. 



The second antennas have retained this original function in greater 

 measure than the first. They consist of a stout cylindrical basal por- 

 tion, which is also produced backward near the median line into a 

 blunt chitin spine similar to that on the first antenna? and right in line 

 behind it. 



Sometimes this spine is reenforced by another situated just anterior 

 to it, the two and the spine on the proximal basal joint of the first 

 antenna forming a row alongside the median line (maeulosus, amerl- 

 camis). The remaining three joints of these second antennae are much 

 narrower than the basal one and the terminal joint is also very short. 

 They are all, including the l)asal joint, armed with a few bristles on 

 their anterior surfaces at the 



IX Argulds 



AMKRICANUS. 



distal ends. The three termi- 

 nal joints are usually fiexed 

 posteriorly until they form a 

 right angle with the basal joint. 



The anterior maxillipeds in 

 all adult Arguli are modified 

 into sucking disks. This also, 

 as can be seen from the on- 

 togeii}', is a derived or ac- 

 quired character. 



The function of prehension 

 is of course the same whether 

 the appendage end in a claw or a sucking disk, but with the growth of 

 the disk comes a secondary function of walking or scuttling about over 

 the surface of the fish's body. For this the disk is much better suited 

 than a terminal claw; the latter gives as firm a hold when once fixed 

 in the fish's skin, but does not admit of adjustment rapid enough to be 

 used as an organ of locomotion. These disks consist of a short cylin- 

 drical l)asal portion, representing the basal joint of the original larval 

 appendage, and a terminal border of nearly twice the diameter. 



The latter does not represent the terminal joints of the original 

 appendage, l)ut seems to be a new growth after the absorbtion of those 

 joints. In the larval development these joints persist for a long time 

 as a useless appendage attached to the side of the maxilliped between 

 the base and the border, and they seem to be gradually absorbed and 

 used in making the border, much as the tadpole's tail is used to make 

 the hing legs of the little frog. The Ijorder is largely membraneous, 

 is serrated around the edge, and is strengthened hy numerous rays which 



