NATURE OF THE DRACUNCULUS, OR GUINEAWORM. 113 
about sgeth of an inch in diameter, but anteriorly and posteriorly are reduced to Tooth 
of an inch. 
The lateral vessels are very much smaller, being only about ggpgth of an inch in 
diameter, and near the extremities of the body not more than 415355th of an inch. They 
are situated outside the nervous cords, and may be seen through their substance pur- 
suing a gently undulating course and having a uniform double contour (Pl. XXI. fig. 26). 
These vessels may sometimes be seen lying on the integuments after the nerve has been 
stripped off, and on one occasion I saw the broken extremity of a vessel distinctly pro- 
jecting alone from the membrane on which it was lying. 
In the specimens of Guineaworm examined by Mr. Busk, he did not discover any 
vessels in the situations I have described, but alludes to what appear to be four lacunar 
canals, one on each side of the dorsal and ventral muscular bands, in the middle of 
peculiar tracts of granular substance. I have met with nothing corresponding to this 
in the specimens examined by myself. 
What I have described as dorsal and ventral vessels in the Guineaworm, correspond 
in position and general appearance with the dorsal and ventral nerves of Blanchard, 
Cloquet, and other anatomists, in Ascaris lumbricoides; but when portions of these 
structures are submitted to the microscope and examined by transmitted light, they are 
found to present important differences. 
In Ascaris we find a tube with irregular swellings at varying intervals, composed 
of a delicate investing membrane, closely packed with small, roundish, highly refracting, 
fatty-looking particles. The well-known lateral cords in the same worm are three or 
four times as thick as those just described, and present a distinct channel or lacunar 
passage running through their centre, but in other respects are precisely similar, being 
made up, like them, of the same bright fatty-looking particles contained within a homo- 
geneous membrane. I think, however, after the most careful examination, that there are 
also indistinct traces of a lacunar passage in the dorsal and ventral cords. 
I have found four bodies essentially similar to these in Ascaris mystax ; and, according 
to Blanchard, they are to be met with in most Nematoids*. | 
Professor Huxleyt has described, in an Ozyuris of the Plaice, two contractile vessels 
communicating with the exterior and lodged in lateral cellular bands, whieh are doubtless 
homologous structures with those just mentioned as existing in Ascaris. 
There can be little doubt, then, that these lateral cords are in some way connected with 
the development of a water-vascular system; and considering that the dorsal and ventral 
cords have exactly the same histological characters, I see no reason why these latter 
should be held to belong to the nervous system, even had we not the farther evidence 
before us which the Guineaworm presents. But here, in the precise situation of thee 
* Walter (loc. cit.) describes four such bodies in Ozyuris ornata, and "bir ped anis va pto 
He thinks they are in some way connected with the development of the animal, as these structures are — Ee 
and densely crowded with fatty particles when the animal is young, but that the latter gradually disappear wit 
advancing age and maturity. 
T Lect. on Gen, Nat. Hist., Med. Times and Gaz. 1856, vol. ii. p. 384. 
