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THE STRUCTURE AND RELATIONSHIPS OF 
GNATHOSTOMA SIAMENSE (LEVINSEN). 
By ROBERT T. LEIPER, M.B., F.Z.S. 
Helminthologist to the London School of Tropical Medicine. 
The natives of Siam are occasionally affected by subcutaneous 
tumours that have been found to be due to the presence of a small 
nematode worm named by Levinsen (1889) Cheiracanthus siamensis. 
Only one description of the species occurs in literature, and as this, the 
original one, was based upon a solitary immature female it is necessarily 
lacking in many details. 
Recently a specimen was presented to the London School of Tropical 
Medicine by Dr A. F. G. Kerr, who had just returned from Siam. The 
parasite was mounted in Canada balsam and bad become very opaque, 
as frequently happens to nematodes that have been prepared in this 
medium. By prolonged immersion in creosote the balsam was dissolved 
and the worm acquired considerable translucency. It was then evident 
that the specimen was a male, and therefore of very special value as it 
afforded material for a determination of certain important specific 
characters that had been hitherto unobtainable. 
Description of the male worm. 
The specimen measures 10'55 mm. in length, 0'6 mm. in breadth. 
The anterior half is quite straight and terminates in a distinctly 
globular swelling which is separated from the rest of the body by a 
neck-like constriction. The posterior half of the worm is involved in a 
ventral bending that developes into a complete spiral of one and a 
quarter turns before the tip of the tail is reached. 
The globular swelling at the anterior end bears two large fleshy 
lips that guard the mouth. The cuticular covering of this portion is 
