160 A Description of the Thread-worm, Filaria immitis. 



muscular and cutaneous tunics constituted about one-eighth part of 

 the total body diameter, and formed a " tube charnu " to the loosely- 

 lying contained viscera (Plate XXXII., Fig, 13). The mouth was 

 a small circular aperture in the centre of a papilla, occupying the 

 most prominent portion of the rounded anterior extremity of the 

 worm (Plate XXX., Fig. 1, a ; Plate XXXII., Fig. 13, a) ; and the 

 longitudinal muscular layer diverging from it was very strongly pro- 

 nounced. Continuous from this was the oesophagus, about -fo inch 

 in length, and -200 inch in thickness, with strongly pronounced walls 

 made up of a longitudinal and circular muscular layer (Plate XXX., 

 Fig. 1, & ; Plate XXXII., Fig. 13, h). At the junction of the gullet 

 with the stomach was a clearly-defined sphincter. The stomach, or 

 rather alimentary tube, into which the oesophagus opened, expanded 

 from the sphincter into a delicate membranous canal nearly yxju inch 

 in thickness (Plate XXX,, Fig. 1, c), pursued a straight course along 

 the body length of the worm, diminishing at the centre to yio inch, 

 and could be traced to within half an inch of the tail end, where 

 it terminated in a c^cal extremity about 4^ of an inch in diameter, 

 lying between the convoluted ovarian tubes (Plate XXX., Fig. 2, a) ; 

 or, in the case of the male worm, either above or below the sperm 

 duct. Its dehcate wall was made up of very fine longitudinal and 

 circular fibres, and retained within it fat globules and granules, and 

 not uncommonly red colouring matter, doubtless derived from the 

 blood of the host (Plate XXXI., Fig. 6). The alimentary canal 

 was encircled throughout its entire length by the reproductive 

 organs. It will thus be seen that there was no anal aperture, a 

 circumstance possibly connected with the life history of the worm 

 passed within the vascular canals of the host, and with the nutri- 

 ment obtained from a vital fluid comparatively free from efiete pro- 

 ducts ; the alimentary excreta of the parasite being thus reduced 

 to a minimum, if not an actual nullity. In Plate XXX., Fig. 2, 

 the tail end of the female is shown, the outline of the parietes in 

 one aspect being straight, on the other side being comparatively 

 sharply curved, with the result of tkrowing the tip in the direction 

 of the straight longitudinal line of the body — a feature more strongly 

 pronounced in the male. 



The reproductive organs consisted of a vagina opening exter- 

 nally, an uterine canal, and ovarian tubes. The vulva was a small 

 circular or somewhat oval aperture, about ^^ inch in diameter, 

 situated on the anterior end of the worm, generally about A^hs of 

 an inch from the oral aperture, but varying from y^,, inch to, in 

 one instance, 1^ inch from the head. Its presence was with great 

 difiiculty observed in the external surface of the body, even when, 

 as in Plate XXX., Fig. 1, d, it had been clearly traced up from 

 within ; but when detected (from occasionally being surrounded by 

 a somewhat elevated ring of tissue), the cutaneous envelope of the 



