AMERICAN PARASITIC ARGULID.E— WILSON. 



663 



().S5 mm. long, and the larva of Htlzo.^fithil reaches almost 1 mm. (0.9S). 

 And tills, too, in .spite of the fact that the adults of in<</((l<ijt.'< and 

 xthoxtctli'ii are smaller than those of eatosfniii i 'A\\di /<>! laceus. 



That the sizes should l)e thus reversed in the larvie is further good 

 proof of the difiorence in their relative development, i. e. , not only 

 does the greater similai'ity of the appendages to the adult form attest 

 the more advanced development of the stizostetJui larva, but its body 

 is actually nearl}^ twice as large as that of the foUaceus larva. 



All the larva? have the general shape of the adult, save that in 

 foUaceas^ catostonu^ and (intericanus the l)ody is somewhat narrowed 

 posteriorly, while the anal papilhv are nuich larger and terminal 

 instead of l)asal. The carapace is relatively Ijroad and barely covers 

 the bases of the first swimming legs. 



In mtostoiiil the width of the larval carapace is relatively less than 

 that of the adult, but in the 

 other species it is practically 

 the same. Its border is 

 fringed with fine cilia, among 

 which are scattered stouter, 

 seta-lilve tactile organs which 

 are much larger than the cilia 

 and about twice as long. 



The free thoracic segments 

 diminish much more rapidly 

 in these three larv» than in 

 the other two species, but each 

 segment bears a pair of swim- 

 ming legs or their rudiments. 



The abdomen in the three species just named is also very narrow, 

 almost triangular in shape, and terminated by the large anal papillis. 

 In the megalops and stlsostetJdl larvie, on the contrary, the abdomen 

 is as wide as the last thoracic segment, is broadU^ ovate in form, and 

 in the megalopa larva? is terminated by two short, bluntly acute lobes, 

 with the anal papillte at the base of the intervening sinus. In stizo- 

 fitet/ill the abdomen is abruptly truncated posteriorly and the anal sinus 

 is so shallow that there are practically no lobes at all, but the anal 

 papilla? are situated close to the anus, and therefore must be regarded 

 as basal rather than terminal, like those of tnegalojM, to which they 

 also correspond in size. 



The first antenna', and in megalops and stisostethH the second also, 

 ha^'e already assumed nearlv their permanent form. 



In all the species the first antenna are three-jointed,' the l)asal 



^Kellicott says (1880) that the first antennae of stizostethii are four-jointed, but 

 they are really the same as those of the other species. The apparent difference comes 

 from his regarding the basal joint as double rather than single, in which case these 

 first antennae would be four-jointed in all the species. 



4. — First and second antennae of newly 



HATCHED LARVA OF ARGULI'S MEGALOPS. 



