246 



MB, H. A, BAYLIS AXD LT.-COL. CLAYTON LANE ON 



frequently raised into tooth -like prominences in the form of 

 longitudinal ridges, which 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 specially 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 papillae, usually not prominent, is always 

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

 a small pair of lateral papilla?. 



The male possesses more or less well-developed caudal al^e, 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 them 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 

 penetrating to this extent, obtain a very firm hold by burying' 

 their heads 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 Sjyiroxys the caudal ala3 of the male are developed into 

 a "bursa" closely resembling that of Physalo2Uera, in that it is- 

 continued anteriorly across the ventral surface of the body. 



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

 to foi-m a link between Sj>iroxys and such genera as Fhysaloptera 

 and Hahronema. 



(3) In Gnathostoma the ventral surface of the caudal region, 

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

 be compared with the low papilliform processes that cover this- 

 region in FJiysalo'ptera. 



(4) The occurrence, throughout the family, of paired lateral lips 

 suggests close affinity with the Spiruroidea or Spiruridae (see foot- 

 note, p. 247). 



It may be noted here that Stepliens (in Fantham, Stephens, 

 and Theobald, 1916) places Gnathostoma, Tanqua, and Rictularia 

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

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

 bursate nematodes. 



