ENTOZOA 



439 



between the cells were very sharp and straight (fig. 21). In the females this mass 

 of cells lay on the ligament ; in the male, on the other hand, it occupied the centre 

 of the fibrous and muscular strands which compose that body (fig. 25). In the former 

 I could trace no nerves leaving the brain, but in the male two nerves surrounded 

 by muscles pass backward ; these obviously correspond with the retinacula of other 

 forms. 



Classification. 



Until recently the group Acanthocephala included but one genus, Echinorhy^ichus, 

 which comprised several hundred species. Recently, however, Hamann' has pointed 

 out that these species present certain differences which enable him to divide the group 

 into three families, each with a corresponding genus. To these I venture to add a 

 fourth, to include the remarkable form above described. This family may, I think, 

 be called the Apororhynchidae, and the new genus Apororhynchus", which name refers 

 to the absence of the eversible introvert ; and, inasmuch as it is convenient in naming 

 a parasite to have some indication of its host, I think the specific name may be 

 hemignathi. 



If these terms be adopted, the classification of the Acanthocephala will be as 

 follows, the characteristics of each of the first three families being taken from 

 Hamann's papers. 



I. Family Echinorhynchidae. The body is elongated and smooth. The in- 

 trovert sheath has double walls, and the introvert is invaeinated into it. The nerve 

 ganglion is in the introvert sheath, mostly embedded in it and central in position. 

 The hook papillae are only covered with chitin at their apex, and the hooks have 

 a process below. 



Genus Echinorhynchus, with the characters of the family. 



The vast majority of Acanthocephala belong to this family ; a few may be 

 mentioned. E. proteus, found in many fishes and varying in size with its host ; its 

 larval forms inhabit the Amphipod Gainmarns pulex, and are also found in the body- 

 cavity of numerous fresh-water fishes. E. clavula occurs in many fishes and in the 

 intestine of a species of Bitfo. E. angustatus is found also in fishes, with its larval 

 form in the Isopod Asellus aguaticus. E. nionilifor'mis is said to attain maturity 

 in the human intestine; its usual host is a mouse, and its larval host is the larva of 

 a beetle, Blaps niticronata. E. porrigens invests the intestine of the rorqual, and 

 E. strumosus that of a seal. There are many others. 



' Loc. cit. and Zool. Anz. Bd. xv. 1892, p. 195. 



' In my original paper I suggested the name Ar/iyiichiis, but as Professor C. Wardell Styles and Professor 

 A. Hassall have pointed out that this name is preoccupied, having been used by Dejean in 1834 for a beetle, 

 I later (Quart. J. Micr. Sci. xlii. p. 361) suggested the name Apororhynchus. 



F. H. II. 57 



