410 PHYLUM MOLLUSCA. 
Reproductive system.—The sexes are separate, but there 
is not much external difference between them, though the 
males are usually smaller, less rounded dorsally, and have 
slightly longer arms. When mature, the male is easily 
known by a strange modification on his fifth left arm. The 
essential reproductive organs are unpaired, and lie in the 
body cavity towards the apex of the visceral mass. 
The testis—an oval yellowish organ—lies freely in a peritoneal sac, 
near the apex of the visceral mass. From this sac the spermatozoa pass 
along a closely twisted duct—the vas deferens. This expands into a 
twofold ‘‘ seminal vesicle,” and gives off two blind outgrowths, of which 
one is called the ‘‘ prostate.” The physiological interest of these parts 
is that within them the spermatozoa begin to be arranged in packets. 
In this form they are found within the next region, the spermatophore 
sac, which opens to the exterior to the left of the anus. Each spermato- 
7 Phore is like an automatically explosive 
bomb; within the transparent shell 
there lies a bag of spermatozoa, and a 
complex spring-like arrangement. Even 
on the scalpel or slide these strange but 
efficient bombs will explode. The 
liberated spermatozoa are of the usual 
type. 
The ovary—a large, rounded white 
organ—lies freely in a peritoneal sac 
near the apex of the visceral mass. 
From this sac the eggs pass along a 
short direct oviduct, which opens into 
the mantle cavity to the left of the anus. 
Associated with the oviduct, and pouring 
viscid secretion into it, are two large 
‘‘nidamental glands,” of foliated struc- 
. ture. Close beside these are accessory 
glands, of a reddish or yellowish colour, 
with a median and two lateral lobes ; 
while at the very end of the oviduct are 
two more glands. All seem to contribute 
to the external equipment of the egg. 
The en es pass from the 
genital duct of the male to the fifth 
left arm, which becomes’ covered 
with them and quaintly modified. 
This modification of one of the arms 
is usual among cuttlefish; indeed, 
Fic. 220.— Male of Argo- in some, e.g. Argonazita and Trem- 
nauta (after Jatta), show- octopus, the modified arm, with its 
ing ‘‘hectocotylus” arm; load of spermatozoa, is discharged 
compare Fig. 9 of female. bodily into the mantle cavity of the 
