34 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
The male reproductive organs are tlie testes (plate 36, fig. 120), the ducts of which 
open at the base of the last pair of walking legs. The sperm which is inclosed in 
gelatinous capsules or spermatophores, the secretion of the seminal ducts, is thus 
ejected in packets. There is no penis or tubular extension of the integument from the 
opening of the duct, as is the case with the Brachyura. 
The first pair of legs of the tail are also modified in a peculiar way in the male, as 
if.they served for conducting the spermatophores through the elastic, slit-like orifice of 
the seminal receptacle. 
There are numerous secondary sexual distinctions, the most striking of which is 
seen in the abdomen. The latter is conspicuously broader in the female, a variation 
which is correlated with the greater size of the ovary as compared with the testis; 
its lateral plates are deeper and it is more conspicuously hollowed below to form an 
incubatory pouch for the ova. A discriminative fisherman can thus distinguish the sex 
at a glance. (Compare plates 4 and 6.) The large claws are more voluminous in the 
male than in the female, and the male attains the greatest size. This would imply 
that the male molts oftener than the female, which, according to the observations of 
Brook ( 26 ), is actually the case. 
In addition to these distinctions Gouriet ( 82 ) found that in the crayfish the 
antennae were longer in the males than in the females; that while the length of the 
abdomen of the male was relatively shorter, it was heavier than in the female. He 
found the length of the abdomen, compared with that of the carapace, to be in the 
proportion of 7 to 0 in the female, while in the male this difference in length did not 
exceed inch. 
In the male lobster the second pair of swimmerets carries a small spur on its inner 
blade, the function of which is obscure. The reduction of the first pair of abdominal 
appendages in the female is in all probability correlated with their use in reproduction. 
If they were of the normal size they would catch so many eggs at the time of oviposi - 
tion that it would be next to impossible for the female to completely flex the abdomen. 
Locomotion would thus be interfered with, and the eggs would be constantly exposed. 
As it is, it sometimes happens in very large females, where the ova are excessively 
abundant, that it is impossible to completely fold the abdomen. (See p. 54.) 
Each testis consists of a slender, grayish-white, sacculated tube filled with devel- 
oping sperm cells (fig. 120, plate 36), and its coiled duct usually contains sperm in 
abundance. The spermatophore can be easily pressed from the duct, when the latter is 
dissected out. The sperm cells have a characteristic shape (tig. 129, plate 37) and are 
absolutely immobile in the conditions under which they are ordinarily observed, but 
it is impossible to suppose that this is always the case. Their complicated form, 
recalling that of the bell-shaped medusa, leads one to suspect that under the influence 
of some subtle and unknown stimulus, possibly of a chemical nature and coming from 
the cement glands or some other organ, they are able to execute independent and 
rapid movements through the water. 1 
1 Cano states that he once detected amoeboid movements in the rayed sperm-cells of the crab 
Maia. See observations quoted on p. 49. 
