456 



ANNELIDA. 



coloured gland-cells. The circular and longitudinal muscular layers are both 

 thin. Segmental coelomic septa are not present, except the septum between 

 the peristomium and the next segment. Dorsal pores and head pores are not 

 present. One pair of nephridia is present in each of the setigerous segments. 

 The alimentary canal consists of pharynx, oesophagus, and intestine ; and the 

 anus is at the hind end of the body. The central nervous system consists of 

 the cerebral ganglion, which is continuous with the ectoderm of the prestomium. 

 It is said that there is no ventral nerve cord. Generative organs are only 

 occasionally developed, reproduction generally taking place by fission. The 

 testis is median and unpaired, and lies in the fifth segment (the peristomium 

 being the first) ; the ovary is similarly placed in the sixth segment. There 

 are no generative ducts. The sperm escapes by nephridia, the ova by a 

 pore on the ventral side of the sixth segment. Spermathecae are small oval 

 sacs in segments 3-5. At sexual maturity there is a feeble clitellum on the 

 ventral surface of segments 5-7. The oviposition is unknown. One species 

 has the habit of encysting in a chitinous capsule. There are several English 

 species. 



Aeolosoma differs from Oligochaets in the folloAving characters, some of which 

 point to Archiannelidan affinities ; the continuity of the cerebral ganglion with 

 the ectoderm, the absence of a ventral nerve 

 cord, the absence of generative ducts, the 

 cephalic ciliated pits, the absence of transverse 

 coelomic septa ; it resembles them in being 

 hermaphrodite and in having spermathecae 

 (which, however, are found in Saccocirrus). 



It is possible that the marine genus Ctenodrilus 

 (Scharff. Q. J. M. S., 27) should be placed with 

 Aeolosoma. It has one row of comb-like setae 

 on each segment, the prestomium is ciliated on 

 its ventral surface, and bears two ciliated pits. 

 There is only a single pair of nephridia in the 

 peristomium, and only a single layer of muscles 

 longitudinal in the body- wall. The nervous 

 system, which consists of a cerebral ganglion and 

 ventral cord, lies in the ectoderm. The sexual 

 worm is unknown. 



Dinophilus is a small marine worm found in 

 the Channel in the spring on sea- weeds. There 

 is a head consisting of preoral and postoral 

 portions, and a body consisting of five or six 

 segments, each marked externally by one or 

 two ciliated rings. The ventral surface is- 

 ciliated. The anus is posterior, and projecting 

 on the ventral side of it is a kind of tail-append- 

 age. The preoral lobe either possesses two ciliated 

 rings, or is uniformly ciliated : it also bears a pair 

 of eyes and some groups of stiff sensory hairs, 

 and a pair of ciliated pits. 



The alimentary canal is straight and ciliated ; there is a ventral muscular 

 organ opening into the oesophagus like that of Protodrilus. 



The nervous system consists of a ganglion in the preoral lobe, and a pair of 



Fro 362. Dinophilus gigas (after 

 Weldon). an anus; cp cephalic 

 pits; ci transverse ciliated 

 bands ; M mouth ; St stomach ; 

 sh cephalic sense hairs ; sh' 

 post- cephalic rings of sense 

 hairs placed close behind the 

 ciliary rings. 



