ACANTHOCEPHALA. 



297 



develops to a small elongated larva, which, like a pupa, lies in the 

 body-cavity of the small Crustacean, with its proboscis retracted and 

 surrounded by its firm external skin as by a cyst (Fig. 243, b). As 

 stated above, the skin of the larva gives rise only to the integu- 

 ment, the vessels and the lemnisci of the adult ; while all the other 

 organs enclosed within the dermal muscular envelope, viz., the nervous 

 system, the sheath of the proboscis, and the generative organs, are de- 

 veloped from the so-called embryonic nucleus. It is only after their 

 introduction into the intestine of fishes (Ecli. proteus} or of aquatic 

 birds (Ech. polymorplms\ which feed on these Crustacea, that the 

 larvae attain to sexual maturity, copulate, and reach their full size. 



c ^\ d 



a 



FIG. 243. Larvae of Echinorhynchus proteus from Ciammarus (after Leuckart). a, free embryo ; 

 Ek embryonic nucleus. 6, older stage, with more differentiated embryonic nucleus, 

 c, young female worm ; Ov ovary, d, a young male worm ; T testes ; Le lemnisci. 



The numerous species of the genus Echinorhynchus 0. F. Muller, live in the 

 alimentary canal of different Vertebrates, principally fishes, the gut wall of 

 which may be as it were sown with these animals ; the asexual larvae are 

 found in small Crustacea (Amphipods, Isopods). Lambl found a small sexually 

 immature Echinorhynchus in the small intestine of a child which died of 

 leukhaemia. Ech. polymorphus Brenis, in the intestine of the duck and other 

 birds, larva in the crayfish ; E. proteus Westrumb., larval form in Gammarus 

 and in the body -cavity and liver of Phoxinus, sexual form in the trout. 

 Gigantorhynehus Haniann, with ringed and flattened body, intestine of ant- 

 eaters, birds, swine ; larval form in grubs of insects ; G. gigns Goeze, as large 

 as an Ascaris lumbricoides, in the small intestine of the pig, larval form in 

 grubs of beetles. Neorhynchus Haniann, the nuclei of the epidermis and 

 lemnisci are large and few in number, as in the larvae of other forms ; in the 

 carp, larval form in larvae of Neuroptera, etc. Arhynchus Shipley, without 

 eversible proboscis and hooks ; epidermis and lemnisci with giant nuclei ; in- 

 side the skin of a bird Hemignathus procerus. 



