NATURE OF THE DRACUNCULUS, OR GUINEAWORM. 107 
External Characters.—Worms varying in length (Pl. XXI. fig. 1) from eighteen 
inches to three feet, and from yth to sth of an inch in diameter, of a milk-white colour 
(or light straw when kept in spirits), mostly quite smooth, but sometimes slightly annu- 
lated by rugose contractions; cylindrical, or more or less flattened laterally, and 
tapering gradually towards both extremities. About 35th of an inch from the posterior 
extremity the body becomes more abruptly narrowed, and terminates usually in a 
sharply curved tail or point. In some cases, however, the tail is straight, and in others, 
as pointed out by Carter, it is more acutely bent upon itself, and seems connected to the 
adjacent portion of the body by a delicate membrane (Pl. XXI. figs. 4, 5, 6, 7). On 
opposite sides of the body are seen, extending along its whole length, two opaque bands, 
corresponding with the great dorsal and ventral muscles, and two more translucent inter- 
muscular spaces. For a short distance from the anterior extremity, two narrow, white 
lines may also be seen running along the body, each being midway between the lateral 
spaces. No vulva discoverable; anal aperture doubtful—if present, situated in the con- 
cavity of the tail. 
The integuments are so elastic, that the worm may be stretched to nearly twice its 
natural length. 
Examined with a low power of the microscope, the head presents the following cha- 
racters :—Mouth punctiform, about 4355th of an inch in diameter, situated in the centre 
of a somewhat flattened terminal disk, and surrounded by a circular eminence or lip* 
(Pl. XXI. fig. 2) 345th of an inch in diameter. Around the mouth are four papilla, 
two of which (much larger than the others, and also nearer the oral aperture) are con- 
tinuous with the narrow white lines before mentioned, and are therefore situated verti- 
cally; whilst the two lateral, more remote from the mouth, not prominent, and scarcely 
more than opaque spots are situated at the commencement of the gradually widening, 
lateral, intermuscular spaces. The upper and lower papille are prominent, and well 
seen in outline (Pl. XXI. fig. 3), being about j5955th of an inch in height, طامؤع‎ of an 
inch in breadth at the base, and şğgth of an inch apart, whilst the small lateral papillze 
are 735th of an inch apart. The mouth and papille are situated in the midst of an 
opaque, whitish, quadrangular space, about rğpth of an inch from side to side, the papillae 
being situated towards the angles, from which also proceed the two opaque-white, gra- 
dually widening, lateral spaces and two narrow dorsal and ventral lines, which are only 
about 3j55th of an inch widet. Between the white lines surrounding the head may be 
seen longitudinal muscular fibres—the origins of the four longitudinal muscles. 
Integuments.—The integuments of the worm are composed of a transparent, almost 
structureless, chitinous substance, arranged in a number of concentric lamellee, present- 
ing peculiar linear markings. Altogether it forms a very tough and highly elastic 
cylindrical investment. 
Analogy would point also to a deep cellular layer of integument ; and though I have 
. * The circular ruge of Carter. "ges reti 
t It will be seen afterwards that this opaque quadrangular space and four converging lines E z 
quadrangular commencement of the sheath of the alimentary canal and its crucial mesenteric process going (Pl. XXI. 
fig. 13) to the intermuscular spaces. 
