REPOET ON THE NUDIBRANCHIATA. 
63 
planoconvex ; the hinder surface has two facets, one on the left, which is the larger, and 
another on the right ; the anterior surface is convex ; the upper margin rather flattened, 
the other sharp ; the length of the mass from before backwards reached 4 ‘5 mm. by 8*5 
mm. in breadth and 7 '5 mm. in height; the chief efferent ducts project 2 mm. Along 
the upper margin runs the vas deferens, forming several loops and then running straight; 
on the posterior side the vaginal duct is directed upwards from the spermatheca ; on the 
under side, between the mucous gland and the prostate, is the chocolate-grey ampulla. 
The largest portion of the genital mass is formed by the prostate, showing a number of 
cells and holes glimmering through. The sausage-shaped, somewhat curved chocolate- 
grey ampulla, is about 5 mm. long by 1 '5 mm. in diameter. The female branch of the 
hermaphrodite duct opens in or in the neighbourhood of the albuminiparous gland; 1 and 
the uterine duct of the spermatheca (fig. .23, d) also communicates with it. The 
spermatheca (fig. 23, a), with the exception of the region of the ducts, is quite covered by 
the prostate; it is pear-shaped, and 5 '5 mm. in length, yellowish in colour, and filled 
with semen and detritus. Its main external duct, the vaginal duct (fig. 23, h), is thinner, 
and has a rather straight course ; it then increases to three or four times its diameter, 
and ascends, bending outwards, to the genital papilla (fig. 23c) ; the whole length of the 
duct is about 8 mm., of which nearly one-half belongs to the vagina, which is rather thick - 
walled with longitudinal folds within. The other, the uterine duct (fig. 23, dd), rises near 
the last, but is thinner, and forms a descending loop ; when stretched to its full length it 
measures about 10 mm. ; at about the junction of its middle and posterior third is the 
spermatocyst. This last (fig. 23, e ) is short and pear-shaped, 1*4 mm. long; whitish in colour 
and filled with semen, it lies beneath the vas deferens, and upon the upper margin of the 
anterior genital mass ; its thin duct is about as long again as the bladder. The male branch, 2 
which takes its origin from the hermaphrodite duct, is short, and immediately enters the 
prostate, which is very large, and together with the included spermatheca occupies about 
four-fifths of the entire anterior genital mass ; it is whitish, with an even upper surface ; 
the prostatic layer reaches a thickness of 1—1*8 mm. on the posterior side of the sperma- 
theca. From the upper side of the left hand end a small, somewhat flattened, thin-walled 
prolongation (fig. 24, a), about 4 mm. long, issues ; it is the vas deferens ; it then narrows 
and forms a loop, and runs in a straight course to the genital papilla ; this last muscular 
whitish-coloured part of the vas deferens is about 1 cm. in length (fig. 24, 6) ; at the end it is 
wider, and forms the prseputium penis, which has a length of about 1 mm., and at the 
base of which is the round aperture of the retracted glans. That portion of the vas 
deferens which is provided with hooks is quite 7 mm. long ; the hooks appeared to be 
arranged in twenty to twenty-five irregular longitudinal rows (forming quincunces ?), the 
number of rows behind appeared to be hardly greater than in front. The hooks (figs. 
20-22) are of a yellowish colour; their size is variable, the greatest length being T3 mm. 
1 Bergh, loc. cit., Taf. xiii. fig. 13. 2 £ oc . c it., Taf. xiii. fig. 13, i. 
