NO. 1788. 



NORTH AMERICAN EROASILID.^— WILSON. 



275 



Fig. 7. — Second antenna of Er- 

 gasilus centrarchidarum. 



tactile setse. These are sensory in function and if the innervation is 



any criterion they must be highly sensitive. 



These heavily armed first antennae, curving around the anterior 



margin of the carapace, give the parasites a 



peculiar bristling front. And they stand out 



so prominently in most species that they can 



be plainly seen with the naked eye despite 



the small size of the creatures. 



The second antennse are attached to the 



ventral surface just posterior to the bases of 



the first pair. They are made up of four joints in each of the genera, 



but vary greatly in size and shape. Their function is prehensile and 



they terminate in one or more stout claws, or even become chelate in 



some of the males. In the genus Er- 

 gasilus they are enormously enlarged 

 and become long enough to clasp 

 around the gill filaments of the host, 

 thereby holding the parasite securely 

 in place (fig. 7). In the other genera 

 they are plentifully supplied with 

 spines and roughened surfaces so as 

 to secure a firm hold and prevent 

 sHpping (fig. 8). 



The inouth-imrts are peculiar and 

 altogether different from those of any 

 other family of parasites, having more 

 resemblance to those of the free- 

 swimming forms. Most of them are 

 rudimentary, some are usually lack- 

 females of the Bomolochinae one pair is 



abortive in position. They consist of an upper lip, the labrum, an 



Fig. 8.— Second antenna of Bomolochus 



NITIDUS. 



ing, and at least in the 



Fig. 9.— Moutii-parts of Ekgasilus mugilis. Za, Labrum; Z6, labium; md, mandible; wii', first 



maxilla; mx", second maxilla. 



under lip, the labium, a pair of mandibles, a pair of maxillary hooks, 

 two pairs of maxillae, and one of maxillipeds. 



