504 



ZOOLOGY 



the internal division of the ccelome by means of septa is complete. Parapodia 

 and seta? are absent, but the prostomium bears a pair of tentacles (<). Several 

 pairs of simple nephridia are present. The position of the nervous system 

 (Fig. 401) is more primitive than in the Annulata in general ; it is continuous 

 with the epidermis, and not separated from it by mesodermal elements as in 

 most of the others. A pair of ciliated grooves (c. p. ) are probably to be looked 

 upon as organs of special sense. 



The family Polygordiidce includes two genera — Polygordius and Protodrilus. 

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

 dius, and a pair of ciliated pits. The segmentation is only very indistinctly 



marked externally in Protodrilus by circlets of 

 cilia ; 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 groove. 

 _l n t There is a vascular system with dorsal and 



D.V 



Z>erE/bt7wi 



KM'. Cd Cxl.Epthnf 



Fig. 400.— Protodrilus, en- 

 tire animal, int. intestine ; 

 mus. w. muscular append- 

 age of oesophagus ; oes. oeso- 

 phagus. (After Hatschek.) 



Fio. 401.— Polygordius neapolitanus, transverse 

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

 of coelomic epithelium ; Ccel. Epthm.' visceral or 

 splanchnic layer of the same ; Cu. cuticle ; Jhr. 

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

 Epthm. enteric epithelium ; M. PI. muscle-plates ; 

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

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

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

 Biology, after Fraipont.) 



ventral longitudinal vessels. In each segment is a pair of simple nephridia. 

 In Protodrilus there are two ventral nerve-cords, connected together by trans- 

 verse commissures: in Polygordius the cord (Fig. 401, V. Nv. Cd) is single; 

 in neither genus is there any trace of ganglia. The sexes are united in most 

 individuals of Protodrilus, ovaries occurring in all the first seven segments and 

 testes in some of those immediately following. In Polygordius the sexes are 

 separate; the ovaries or testes (Fig. 401, Spy) are developed in the posterior 

 segments. There are no special reproductive ducts. 



The larva of Polygordius is a typical trochophore (Fig. 402), and its meta- 

 morphosis into the adult worm (Fig. 403) takes place as in the Polyclueta in all 

 essential respects. 



Ctenodrilus resembles Polygordius in the ectodermal position of the nervous 



