146 
THE VOYAGE OF H.M.S. CHALLENGER. 
the inside, with a thick epithelium; the diameter of the duct is about 0’5 mm. The 
male branch of the hermaphrodite duct is immediately continued into the vas deferens, 
which follows the same course as in the previous species ; it accompanies the vagina 
and the duct of the mucous gland, and becomes imbedded in or near the outer lip of the 
“genital” furrow, 1 and is continued as far as its anterior end, where it apparently bends 
inwards, crosses through the frontal shield, and becomes again free on its inner side. 
The first 6 mm. of the vas deferens are delicate and whitish coloured ; it then becomes 
about twice as thick and more yellowish coloured, and forms a coil which measured 
11 mm. long by 5 mm. in diameter, and behind is of a rather clearer yellow colour; it 
then continues straight from the place of insertion of the retractor muscle (PI. VII. 
fig. 3, c) for the space of about 6 mm. to the penis (fig. 3, b); when unravelled and extended 
the vas deferens measures some 20 cm. 2 by *4 mm. in diameter ; the difference in colour 
between the prostatic and muscular portions of the duct is not very conspicuous. The 
penis (PI. VII. fig. 3 ,<x) is short and sac-shaped, a little flattened, 4’5 mm. long by 2'5 
mm. broad ; its cavity opens laterally by a slit into the middle of the sac of the dart-gland. 
The prseputium of the penis is like that of the previously described species ; its cavity is 
clothed with a thick yellow cuticle and has strong transverse furrows, it is nearly filled by 
the short thick glans (fig. 3) with its cylindrical truncated prolongation, black on account 
of the hooks (fig. 3). This protrusible end of the vas deferens is l - 6 mm. long by - 35 
mm. in diameter ; the hooks are arranged as usual in longitudinal quincuncial series 
(fig. 4), about twelve or fifteen rows at the base of the protrusible part and fifteen to twenty 
at the point, and more backwards in the interior generally twenty- two to twenty-five ; 
these hooks (fig. 4) were of the usual form, attaining a height of , 035- - 045 mm., dirty yellow 
coloured, inclined to brown upon the base. The portion of the vas deferens armed with 
hooks does not extend backwards beyond the base of the penis ; the whole length of this 
portion is not more than 6 mm. In the last straight portion of the vas deferens (fig. 3, bb) 
the proper seminal duct itself winds down in a cork-screw fashion, but goes straight in the 
other j)arts. The retractor muscle of the penis (fig. 3, c) is rather shorter than in the 
previous species, 3 at least 8 mm. long, and about the same breadth as the vas deferens 
throughout. — The dart-gland covers the largest part of its ampulla with its own 
windings; when unrolled it measured 51 cm. by ‘8-1 mm. in diameter; 4 its structure is 
as above described. The ampulla of the gland has again the same form and structure ; 
its length is 2 '5 cm. and diameter 4 '5 mm. The duct, which takes its rise from the 
anterior end of the ampulla, is coiled, when unrolled it measures 2*5 cm., and is hardly 
thicker than the gland. The strong retractor sacci hastatorii and the protrusors are quite as 
1 At the bottom of this furrow there was a fine longitudinal fold, whose sides were traversed by other folds ; a 
similar condition was found by Semper (loc. cit., Taf. xxii. fig. 20) in Onchidium glabrum. 
2 Semper (loc. cit., p. 259) describes the length of this portion as being over 20 cm. 
3 According to Semper (loc. cit., p. 259, Taf. xxii. fig. 10, rp.), the retractor muscle of the penis is much shorter. 
4 Semper (loc. cit., p. 259), in a specimen measuring 5 cm., found the gland to have a length of 80 cm. 
