246 ME, H. A. BAYLIS AND LT.-COL. CLAYTON LANE ON 



frequently raised into tootli-like prominences in the form of 

 longitudinal ridges, wliicli either meet or interlock with those 

 of the other lip. 



The oesophagus, in all the genera, is of a simple club-shaped 

 type, increasing gradually in diameter from before backwards, 

 muscular throughout, and without speciallj'^ modified regions such 

 as a bulb, gizzard, or glandular portion. In some species it is of 

 considerable length, measuring up to about one-fifth of the total 

 body-length. The usual valves are present at its opening into 

 the intestine. 



A pair of cervical papillte, usually not prominent, is always- 

 present in both sexes, and the tail of the female is provided with 

 a small pair of lateral papilla?. 



The male possesses more or less well-developed caudal alse, and 

 two spicules are always present. The latter may be equal, sub- 

 equal, or markedly unequal in length. In the majority of cases 

 they have a characteristic ornamentation. 



The species of all the genera are parasitic in the alimentaiy 

 canal of their hosts, usually in its anterior part, and show a 

 greater or less tendency to adopt a habit of burrowing in the 

 tissues. Some of themi are not infrequently found buried com- 

 pletely in the stomach-wall, where tumours tend to be formed 

 round them at the expense of the host. Others, while not 

 peneti^ating to this extent, obtain a very firm hold by burying 

 their lieads in the mucous membrane. One genus (Gnathostoma) 

 has been found as a, rare, and probably abnormal, parasite of 

 man, its habitat in this case being the subcutaneous connective 

 tissue and not the alimentary canal. 



As indications of possible affinities outside the family, the 

 following points are of interest : — 



(1) In iSpiroxys the caudal alse of the maJe are developed into 

 a "bursa" closely resembling that of Physcdoptera, in that it is- 

 continued anteriorly across the ventral surface of the body. 



(2) The genus Hartertia Seurat, 1915, appears, in some respects, 

 to form a link between Spiroxys and such genera as Physaloptera 

 and Hahronema. 



(3) In Gnathostovia the venti-al surface of the ca-udal region, 

 in the male, is partly covered with spinous processes, which may 

 be compared with the low papilliform processes that covei- this 

 region in Fhysalo'ptera. 



(4) The occurrence, throughout thefamilj^, of paired lateral lips 

 suggests close afiinity with the Spiruroidea or Spiruridse (see foot- 

 note, p. 247). 



It may be noted here that Stephens (in Fantliam, Stephens, 

 a.nd Theobald, 1916) places Gnathostoma, Tanqua, and Rictnlaria 

 in this family. Wedl (1862) also placed Eicf.idaria near the 

 Cheiracanthidea, Hall, however (1916), places it among the 

 bursate nematodes. 



