230 LAND AND FRESHWATER 
is very long, extending forward between the inverted eye-tentacles, 
forming a loop among the muscles of the buccal mass. 
«The penis is bent on itself at the point where the retractor muscle 
is given off (Pe. fig. 4): and a short, blunt, rounded portion extends 
beyond the insertion of the vas deferens (pd.) corresponding to the 
flagellum in some species, or the Kalksack of Semper (the czecum 
ealciferum vasis deferentis). 
“The retractor muscle of the penis has its attachment, together with 
the eye-tentacles, in the usual position, close below the apex of the 
shell, near the posterior margin of the body-cavity (plate xxiv. 
fig. 3 m).” 
Detailed Anatomy of Penis of A. gigas (plate xxvi. figs. 2, 3).— 
“On the removal of the outer sasenlens nevi the ann end isofa 
hollow cone-shape (a), which, on being cut away, presented within a 
cup-shaped depression (a’), and exposed the duct of the penis. It 
contracts Se eoaNs and continues as a smooth stout tube of equal size 
for about 0°25 inch, where it expands again (6) into a stouter portion 
of cylindrical form, “which is 0°55 inch long, Sa continues, with gra- 
dually lessening thickness, up to the part where it is turned suddenly 
backwards, and close to where the retractor muscle is given off (c). 
On removing the outer layer a chitinous sheath was exposed lying 
against the thin membrane beneath (b' 6); and following this down, 
it was found to be the basal end of the spermatophore, with the 
peculiar cervicorn processes at the base, in situ where developed. 
On opening the membranous sac, it was found to consist of one con- 
tinuous thread coiled down on itself (fig. 3), and pressed closely 
together, and was in such good preservation as to be easily unravelled. 
il drew out and measured a portion 51, inch in length, and found it 
to contain 15:1 inches; the whole length of this part being 0°55 
inch in length, would give nearly 7 feet for the total contents of 
the sac. It is,in faet, a spermatic thread of hardened spermatozoa, 
poured out from the vas deferens *. 
“ On further examining the part near c, this cylindrical portion 
was found to end in a conical cap, which again gave off a thin rod, 
which bending sharply back, is evidently in communication with 
the extension of the vas deferens towards d. Behind the junction 
of this Jast is a short gland rounded at the end (e), which contained 
some very microscopic transparent crystalline bodies of oval form 
(fig. 2a). This is the Kalksack mentioned above, and secretes the 
material for the formation of the spermatophore. 
“ This spermatophore, which is an organ of a very complicated and 
curious form, may be thus described :—The basal or anterior end 
consists of a chitinous strap about 0-+ inch long, with the sides more 
or less turned over, forming a sort of trough or long spout, which, 
after it has passed into the ‘spermatheca of the other individual, will 
be found opening into the lower part of the oviduct. At the other 
eud the sides at last meet and form a tube; it then thickens and 
* “This thread is similarly described by M. Baudelot, Ann. Sci. Nat. 1868, 
p. 165, in his description of the capriolus of Arion rufus.” 
