1 64 IVOR MS. 



Class ACANTHOCEPHALA. 

 For a single genus Echinorhynchiis, whose larvae live in Arthropods, 

 and the adults in Vertebrates, a special class, Acanthocephala, has 

 been established. We may provisionally place this genus, virhich has 

 about a hundred species, beside Nematodes, but the relationship does 

 not seem to be very close. Mouth and gut are absent. The anterior 

 end bears a protrusible hooked proboscis. 



Echinorhynchm proteus of Pike, larva in the Amphipod Gammaruspulex. 

 ,, angustalus of Perch, larva in the Isopod Asellus aqua- 



ticus. 

 )) gig"-^ of Pig> larva in young Cockchafers. 



FOURTH SERIES OF " WORMS "—Annelids. 



In the earthworm, and in the common marine Nereids, we 

 at once recognise that the body is divided into a series of 

 rings. But these are not merely external markings, they 

 represent genuine segments or somites of the body. For 

 each segment there is usually a pair of ganglia on the ventral 

 nerve-cord, and a pair of excretory nephridia. 



We begin with the bristle-footed worms (Chaetopoda), 

 with the familiar earthworm and the marine lob-worm as 

 types. To these must be added certain remarkably larval 

 worms, which probably deserve their name of Archi-Annelids. 

 Very different are the degenerate parasitic Myzostomata 

 which form galls on Crinoids. Divergent but yet with the 

 essential Annelid features are the leeches (Discophora). 

 Finally, some zoologists provisionally include Sagitta in 

 this series as an Annelid with three segments, and also 

 the Rotifers, since they somewhat resemble the larvae of 

 Annelids. 



Series of Annelids. 

 Class Ch^topoda. Worms with bristles. 



Oligochseta, e.g.. Earthworm. 

 Polychseta. Marine Worms. 

 Echiuridse, e.g., Echiurus, Bonellia. 

 To the class of Chsetopods are appended — 

 (i) The primitive Archi- Annelida. 

 (2) The parasitic Myzostoniata. 



