182 



NEMATHELMINTHES 



present differences which enabled him to divide the group inl 

 three families, each with a corresponding genus To these I 

 have ventured to add a fourth family, to include a remarkable 

 species, Arhynchus hemignathi, described below. The char- 

 acters of the first three families in the account given below are 

 taken from Hamann's paper. 



Family I. Echinorhynchidae. The body is elongated and 

 smooth. The proboscis-sheath has a double wall, and the pro- 

 boscis is invaginated into it. The 

 central nerve -ganglion lies in the 

 middle line, as a rule on the pos- 

 terior blind end of the proboscis- 

 sheath. The papillae which bear the 

 hooks are only covered with a chitin- 

 ous cap at their apex, and the hooks 

 have a process below. This family 

 is by far the largest ; a few species 

 only can be mentioned. Echirwrliyn- 

 chus proteus lives in its mature form 

 in fishes ; the young forms, up to a 

 centimetre in length, are found living 

 freely in the intestine of numerous 

 fresh-water fishes. Those found in 

 Gobio fiuviatilis, the gudgeon ; Leu- 

 ciscus virgo; Lota vulgaris, the burbot 

 or eel-pout ; young trout ; Thymallus 



Fig. lOO.-Fully formed larva of Vfi^ the g^yling, seldom Sur P asS 



EcMnorhynchus proteus from this size, but those found in Acerina 



the body - cavity of Phoxinus 

 laevis. (From Ham ann.) Highly 

 magnified. a, Proboscis ; b, 

 bulla ; c, neck ; d, trunk ; e, 

 e, lemnisci. 



cernua, the pope fish ; in Abramis 

 bipunctatus ; in Esox lucius, the pike, 

 and in older trout, attain or surpass 

 double the length. As the parasites 

 grow older they bury their proboscis and neck in the wall of the 

 intestine, the inner surface of which is studded with the orange- 

 coloured bodies of the parasites. The proboscis is so deeply 

 sunk in the wall of the alimentary canal as to form a papilla 

 on its outer surface (Fig. 92). The larvae of E. proteus are 

 found in the body-cavity of Gammarus pulex, one of the Aniphi- 

 pod Crustacea, and also in the same position in numerous fresh- 

 water fishes ; they must have passed into this first host by the 



