PHYLUM ANNULATA 



403 



the coelome by means of septa is complete. Parapodia and setae are absent, 

 but theprostomium bears a pair of tentacles (t). Several pairs of simple nephridia 

 are present. The position of the nervous system (Fig. 367) is more primitive than 

 in any of the rest of the Annulata, with the exception of the Archi-Chsetopoda ; 

 it is continuous with the epidermis, and not separated from it by mesodermal 

 elements as in the others. A pair of ciliated grooves (c. p.) are probably to be 

 looked upon as organs of special sense. 



The Histriodrilidce are minute worms which live as parasites on the lobster 

 (Astacus), feeding on its eggs. The body consists of only about eight narrow 

 segments. The head has sensory tubercles and two short processes having the 



function of limbs : a similar but larger pair of 

 limbs occurs on the last segment of the body. 

 The alimentary canal consists of oesophagus, in- 

 testine, and rectum ; the oesophagus contains 

 three horny jaws. A pair of closely united cere- 

 bral ganglia are situated in the prostomium, and 

 are connected behind by cesophageal connectives 



D.V 



FIG. 366. Protodrilus, en- 

 tire animal, int. intestine ; 

 mu3. re. muscular append- 

 age of oesophagus ; <v.s. oeso- 

 phagus. (After Hatschek.) 



FIG. 367. Polygordius neapolitanus, transverse 

 section of a male specimen. Cod. Epthm. parietal layer 

 of ccelornic epithelium ; CoeL Epithm.' visceral or 

 splanchnic layer of the same ; Cu. cuticle ; J)er. 

 Epithm. deric epithelium ; D. V. dorsal vessel ; Ent. 

 Epthm. enteric epithelium ; M. PL muscle plates ; 

 0. M. oblique muscles ; Spy, immature gonads ; 

 V. Nr. Cd. ventral nerve cord continuous with deric 

 epithelium; V. V. ventral vessel. (From Parker's 

 Biology, after Fraipont.) 



with a ventral cord, which is dilated into a ganglion in each segment. There 

 are foar pairs of simple segmental organs in the female, five in the male. 

 The sexes are separate ; the gonads, whether ovaries or testes, are formed by the 

 germination of the visceral layer of the peritoneum. Genital ducts are present 

 in both sexes. 



The family Polygordiidce includes two genera Polygordius and Protodrilus. 

 There are a pair of prostomial tentacles, long in Protodrilus, short in Polygor- 

 dius. The segmentation is only very indistinctly marked externally in Proto- 

 drilus ; in Polygordius it is indistinct in front, but better marked behind. In 

 Polygordius lacteus a series of tooth-like processes occur round the anus, and in 

 front a circlet of adhesive papillae. In Protodrilus there is a ventral ciliated 



