1922.] 



H. A. Baylis and R. Daubney: Parasitic Nematode*. 



:u\ 



entirely absent in the adult female, or reduced, as in the Mermithidae, to a more or less solid organ 

 functioning as a reserve of food-material. Again, in all these forms the female genital apparatus is 

 reduced to a single uterus and ovary. The vulva, however, is not anteriorly but posteriorly situated. 

 The worms are either protandrous hermaphrodites, or the sexes are separate, only the females and 

 young larvae being parasitic. A position in some respects intermediate between the present form and 

 the group referred to might perhaps be assigned to the genus Aproctonema, Keilin, 1917. This is 

 represented by A. entomophagum, Keilin, of which the separate sexes are both parasitic in the larvae 

 of a Dipterous insect. The oesophagus of Aproctonema has a somewhat similar structure to that of 

 Scolecophilus. The intestine (which has an anterior diverticulum), is a solid " fat-bod}- ", and has no 

 posterior opening. There are two opposed uteri in the female, and the vulva is situated somewhat 

 behind the middle of the body. 



A sac-like vestige of the second uterus, somewhat like that described above for Scolecophihis, 

 has been observed in Sphaerularia, and also in some of the free-living " monodelphic " forms. It 

 appears in some cases to act as a receptaculum seminis rather than a reservoir for developing eggs, but 

 possibly it serves both purposes. 





Forms of free-living (Anguilltjlid) Type. 

 Genus Cephalobus, Bastian^ 1865. 

 Cephalobus seistanensis, sp. nov. 



(Figs. 72, 73.) 



A number of minute nematodes were collected by Dr. N. Annandale and Dr. S. W. 

 Kemp from the tissues of the water-snail, Gyraulus convexiusculus, in reed-beds in 

 the Hamun-i-Helmand, Seistan, E. Persia. These specimens 

 may have been in the pulmonary cavity. They had a reddish 

 colour when alive, like that of the blood of the mollusc. 

 They probably belong to the genus Cephalobus, of which one 

 member, C. biltschlii de Man, is known to be, at least at times, 

 a parasite of certain fresh-water snails (Succinea), though most 

 of the species are free-living or to some extent parasites of 

 plants. 



The present species has a length of 0*95-1 "o8 mm. in the 

 male and 1*3-1*43 mm. in the female. The maximum 

 thickness of the male is about 0*025 mm., of the female 0035 

 mm. The oesophagus is from 0*2 to 027 mm. long, and is 

 composed of a long anterior muscular portion, narrow ante- 

 riorly and posteriorly, but somewhat swollen for about the 

 middle third, and a rather elongated, fusiform, posterior 

 glandular portion, or bulb, of larger diameter. This bulb 

 is not distinctly marked off from the rest of the oesophagus. 

 The nerve-ring surrounds the muscular portion at the back 

 of its swollen middle region. 



The caudal end of the male is strongly coiled ventrally. 

 The tail is 0*05 mm. in length and tapers sharply to a fine 

 point. There are two equal, broad spicules, 0026 mm. long, 



Fig. 72.- 



istanensis. 



-Cephalobus se- 

 Anterior end. 



