158 



NEMATHELMINTHES 



Here must be mentioned two families closely allied to the 

 true Nematodes. 



(i.) Chaetosomatidae. This family 

 includes three genera : Chaetosoma, 

 Rhabdogaster, and Tristicochaeta. Ac- 

 cording to Metschnikoff, 1 although they 

 are not true Nematodes, they have 

 a great likeness to the group. Ke 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- nne hairs, and on the ventral surface, 



^ f r(mt Q f t 



57. (From Metschnikoff.) a, 



row or about fifteen cylindrical pro- 



Oesophagus ; b, intestine ; c, 



anus; d, ovary; e, generative n'ppHrms 

 pore ; /, ventral bristles. J 6Cl 1On8 ' 



whose 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-jveeds in the neighbour- 

 hood of Salerno. 



The genus Tristicochaeta 2 differs 

 from the foregoing in having three rows 

 of locomotor projections instead of two. 



Rhabdogaster has no head distinct 

 from the body, though the anterior 

 part of the body is swollen. A 



Second swelling OCCUrs, as is also the FIG. 80. Tristicochaeta irutri- 

 ., , .~ T . , . mense Pauceri, in one of its 



case with Chaetosoma, in the region most usual portions, showing 



the triple row of ventral 



bristles, x 100. From Pauceri.) 



of the opening of the genital ducts. 



. 7 & . . 



The female in Rh. cygnoides attains a 



length of 0'36 mm. In this genus the hairs are confined to 



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



2 Panceri, Atti Ace. Napoli, vii. 1878, No. 10. 



