AMERICAN PARASITIC ARGULIDM— WILSON. 



685 



unfortunate that Claus's tigure should have become the classic for all 

 text-books, encyclopedias, and dictionaries. It does not show any of 

 the segmentation in the swimming legs correctly, and without the 

 accompanying text manifestly places its author in error. 



Both exopods and cndopods are furnished with two rows of long 

 plumose seta? along the dorsal and ventral edges of their posterior sur- 

 face, which render them efficient oars for propulsion through the water. 

 Similar shorter setfe are found along the posterior Ijorder of both 

 basipod joints of the posterior legs, and in some species {/naculosus, 

 'Versicolor, etc.) along the basipods of all the legs. Often, also, the 

 entire surface of the boot-shaped appendages of the basal joints of the 

 posterior legs will be found covered with these seta?. 



More than half the species (17 out of 26) have an appendage called 

 a fiagellum {Gelsselanhang) attached to the two anterior pairs of legs. 

 This consists of a slender shaft attached to the distal end of the basi- 



FiG. 15.— Posterior swimming leg of Argulus americakus; the arrangement of the muscles 



SHOWS CONCLVSIVELY THAT THE EXOPODITE IS NOT JOINTED, AND THAT THE ENDOPODITE HAS BUT 

 A SINGLE JOINT. 



pod, just above the base of the endopod. At first it is directed outward 

 parallel to the endopod, but is Ijent abruptly upward and inward, so 

 that it lies along the dorsal surface of the basipod. 



It also carries two rows of plumose seta? and is capal^le of inde- 

 pendent motion. There can be little doubt that one at least of its 

 functions is to keep the ventral surface of the carapace clean and to 

 remove any foreign particles that might find lodgment between the 

 legs and carapace. The blood enters the main shaft of these flagella 

 just as it does the exopods and endopods of the swimming legs, but 

 can not of course get out into the seta?. This coupled with its very 

 small size renders it difiicult to see how such an appendage can serve 

 any important respiratory function. 



In the females of many species we find a pair of long finger-like 

 papillge, situated one on either side of the opening of the oviduct 

 between the bases of the posterior pair of legs. 



