392 THOS. H. MONTGOMERY jr., 
Outer cuticula of the male. The areolar layer is lacking 
on the mid-ventral line of the whole trunk, as in the female, on the 
iiedio-ventral surfaces of the tail lobes (Pl. 39, Fig. PI. 40, Figs. 43, 47, 52), 
and the anterior and ventro-lateral surfaces of the head. In the regions 
where the areolar layer is lacking, except on the head, the homogeneous 
layer of the cuticle shows a differentiation of elevated tubercles (Tub 
Figs. 43, 42, Pl. 39; Figs. 47, 52, Pl. 40). These are limited to the 
mid-ventral region of the trunk and the inner surfaces of the tail 
lobes (Pl. 43, Fig. 85). Their height, arrangement and number varies 
in different individuals. They are largest and most numerous just 
anterior to the cloacal aperture; on the ventral surface of the trunk 
they are sometimes arranged in two rows, one on each side of the 
median line (Zub Figs. 83, Pl. 42; Figs. 86—89, Pl. 43). Each larger 
tubercle consists of a base formed by a thickening of the homogeneous 
layer of the cuticle, and the tubercle proper which is imbedded in and 
projects above the latter (Pl. 39, Fig. 43; Pl. 40, Figs. 47, 52); the 
homogeneous layer of the cuticle (H. Cut) does not cover the projecting 
portion of the tubercle. The substance of the tubercle proper is 
yellowish and hyaline naturally (Fig. 44), but with the iron-haemato- 
xylin stain it colors more deeply than the homogeneous layer of the 
cuticle (Figs. 43, 47, 52 Tub). Anterior to the cloacal aperture each 
tubercle is somewhat finger-shaped, and often several tubercles are 
. closely grouped upon one base, as the teats upon the udder of a cow 
(Figs. 44, 89 Tub). Basally each tubercle sends branching roots into 
the fibrous cuticula (the cuticula has no areolar layer where these 
tubercles occur), some of which pass inwards almost to the hypodermis, 
while others bend at an angle and course between the fibrous layers 
(Pl. 39, Fig. 43; Pl. 40, Figs. 47, 52). I was unable to find any con- 
nection of nerve fibres with such processes. Only with the iron- 
haematoxylin stain can these roots be seen clearly, and then very 
sharply; though these tubercles thus extend into the fibrous cuticle, 
they would seem more properly to belong to the outer cuticle. 
There is thus a well-marked sexual difference in the structure of 
the outer cuticle. The male alone shows the tubercles so characteristic 
of the genus Chordodes (but not the club-shaped processes of the 
latter), but only upon the cuticle of the ventral surface and the inner 
sides of the tail lobes. The function of these tubercles has not yet 
been explained, though they have been used to very great extent as 
distinctive characters by the systematists. They might aid the sense 
of touch, might serve to hold copulating individuals more firmly 
