144 BULLETIN OF THE 
hand, it measures from 5 to 10 w in thickness. It is highly refractive, 
and similar to chitin, although not identical in composition with that 
substance, since it may be easily dissolved in boiling KOH. Occa- 
sionally one notes a fibrous or lamellar structure, the layers being par- 
allel to the surface. In most places an outer extremely thin layer may 
be easily distinguished from the subjacent portion by its higher refract- 
ive power. The inner surface of the cuticula is not always even and 
clearly marked off from the hypodermis, but frequently shows a jagged 
outline with underlying granules, which decrease rapidly in size toward 
the muscular layer. 
On the front and upper surface of the head one finds occasional fine 
pore canals, and in total preparations short hairs were seen, but no 
connection between the two could be established. In the hollow pro- 
duced by the ventral flexion of the posterior end, the cuticula displays a 
curious peculiarity. The highly refractive outer layer remains intact, 
but the inner layer is, as it were, bored with conical holes, into which 
the hypodermal tissue projects. These probably represent sensory or- 
gans, but in spite of the proximity of the anal ganglion a nervous supply 
could not be demonstrated. 
There are present as structures of undoubted cuticular origin the 
hairs or bristles of the lines and peculiar scales found along the posterior 
portion of the body of the male. 
Tlte bristles (Fig. 72) form a double row along the dorsal and ventral 
lines, beginning only 0.2 mm. behind the transverse partition which cuts 
off the anterior chamber, and extending to within 0.5 mm. of the pos- 
terior end of the body. The two rows are only 15 to 25 yp apart, 
and the bristles stand opposite each other (Plate II. Fig. 12) at regular 
intervals of 10 4. Normally they are entirely unconnected by any web 
of tissue or mucus. They are, moreover, but lightly attached to the 
cuticula, and hence easily broken off, so that even in the living animal 
it is rare to find any considerable tract perfect. One can usually see the 
scars that have been left, and apprehend from these the normal rela- 
tion of the bristles. Each bristle is, when perfect, about 0.3 mm. long 
and hollow, having in cross section (Fig. 13) an external diameter of 5 
and an internal one of 2». The base is slightly enlarged, and rests on 
the cuticula (Fig. 13), from which in sections it is separated by a defi- 
nite line of demarcation. From the base the bristle tapers very grad- 
ually to a fine point. Its cavity is simply rounded off at the base, 
being separated from the cuticula by a thin layer; toward the point its 
cavity gradually disappears. These structures are, then, entirely super- 
