ANNULOSA: GORDIACEA. 



243 



tile proboscis, which is covered with tranverse rows of recurved 



hooks, and by means of which the parasite attaches itself to 



the wall of the intestine of its host. The integument (c c) is 



highly muscular, and the proboscis is 



contained within a strong muscular 



sheath, and can be retracted by special 



muscular bands (m m). At the base of 



the proboscis is placed a single nervous 



ganglion, and its hinder extremity is 



prolonged into /, the so-called "liga- 



mentum suspensorium," a fibrous band, 



which supports the generative organs, 



The sexes are in different individuals. 



The water - vascular system is in the 



form of subcutaneous reticulated canals 



which are connected with two saccular 



organs or "lemnisci" (b V), placed on 



each side of the base of the probos- 



cis, but the vessels of this system do 



not appear to communicate with the 



exterior. 



The order Acanthocephala includes 

 only one genus, T\2x&z\y,Echinorhynchus, 

 the genus Koleofs being doubtfully 

 referred here. All the Echinorhynchi 

 inhabit in their adult condition the in- 

 testines of fishes, birds, or mammals, 

 and they pass through a metamorpho- 

 sis. The eggs are swallowed by crusta- 

 ceans or insects, and give exit to free 

 vermiform 'embryos, armed with hooks. 

 These burrow out of the intestine of 

 their host and encyst themselves in its 

 tissues, not becoming finally developed 

 till their bearers may be eaten by some 

 vertebrate animal. Thus, the embryos of Echinorhynchus gigas 

 of the pig inhabit the larvae of the cockchafer ; whilst those 

 of E. angnstatus, of Cyprinoid fishes, live in the interior of 

 fresh-water Crustaceans. 



ORDER II. GORDIACEA. Vermiform Scolecida, parasitic in 

 insects during a portion of their existence. An imperfectly de- 

 veloped alimentary canal or none. Water-vascular system rudi- 

 mentary or absent. Sexes distinct. 



The -Gordiacea, or " Hair-worms," are thread-like Scolecids, 

 often singularly like hairs in appearance, which live in the 



Fig. 119. 



larged about twelve times ; 

 Proboscis ; n Neck ; s Mus- 

 cular sheath of the proboscis ; 

 g Ganglion ; b b "Lemnisci," 

 sacs connected with the wa- 

 ter-vascular system ; / Liga- 

 mentum suspensorium ; in m 

 Retractor muscles of the pro- 

 boscis ; t t Testes ; v Vesi- 

 cula seminalis ; c c Integu- 

 ment. (After Leuckart.) 



