34 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



The male reproductive organs are the testes (plate 36, fig. 120), the duets 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 abdomeu. 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 often er than the female, which, according to the observations of 

 Brook (26), is actually the case. 



In addition to these distinctions G-ouriet (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 in the female, while in the male this difference in length did not 

 exceed -£% inch. 



In the male lobster the second pair of swiminerets 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 (fig. 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 lie once detected amoeboid movements in the rayed sperm-cells of the crab 

 Maia. See observations quoted on p. 49. 



