158 



NEMATHELMINTHES 



Here must be mentioned two families closely allied to the 

 true Nematodes. 



(i.) Chaetosomatidae. This family 

 includes three genera : Chaetosoma, 

 Rhaodogaster, and Tristicochaeta. Ac- 

 cording to Metschnikoff, 1 although they 

 are not true Nematodes, they have 

 a great likeness to the group. He dis- 

 tinguishes them from the swimming 

 members of the group as " creeping 

 Nematoda," Chaetosoma, of which 

 two species are known, C. ophicephalum 

 and C. claparedii, has a head distinct 

 from the body (Fig. 79). The mouth 

 is at the anterior end, surrounded 

 by a double semicircle of movable 

 spicules ; the whole body is covered by 

 fig. 79. Mature female of Chae- fine hairs, and on the ventral surface, 



tosomaclapar^iiMetschnl, x j ust i n f ront f the anug ig a double 

 57. (From Metschmkoff.) a, J ' 



Oesophagus ; b, intestine ; c, row oi about fifteen cylindrical pro- 

 anus ; d, ovary ; e, generative i ee ^i ns bv 

 pore ; /, ventral bristles. * ' * 



w T hose agency 

 the animal creeps. The female C. 

 claparedii is 1'5 mm. long, the male 

 1*14 mm. They were found creeping 

 about on sea-weeds in the neighbour- 

 hood of Salerno. 



The genus Tristicochaeta 2 differs 

 from the foregoing in having three rows 

 of locomotor projections instead of two. 



Rhaodogaster has no head distinct 

 from the body, though the anterior 

 part of the body is swollen. A 



Second Swelling OCCUrs, as is also the FlO. 80. Tristicochaeta inari- 

 .,._,., . J , . mense Panceri, in one of its 



case with Chaetosoma, m the region 



of the opening of the genital ducts. 

 The female in Rh. cygnoides attains a 



most usual positions, showing 

 the triple row of ventral 

 bristles, x 100. (From Panceri.) 



length of 0'36 mm. 



In this genus the hairs are confined to 



1 Zcitschr. wiss. Zool. Bd. xvii. 1867, p. 539. 



2 Panceri, Atti Ace. Napoli, vii. 1878, Xo. 10. 



