Sexes in the Genus Paludina. 87 
firming the conclusion already arrived at, namely that males 
can, in this species of Paludina, be distinguished from females 
by their smaller and less ventricose shells and by their right 
tentacle being hooked. 
Of the seventy-six specimens thirty proved to be males, and 
forty-six females; the latter sex thus greatly predominated 
in the series collected; but whether this predominance would 
be maintained in a much more extensive series is to be doubted, 
especially as the tendency of most collectors of zoological 
specimens is to take the fine and to leave the small and juve- 
nile individuals of a species. In each set there occurred only 
a single aged individual, with the apex of the shell much 
eroded. Of the forty shells classed as females a few young 
ones, with the peristome still thin and fragile, and in size 
equal to and less than males of average proportions, cannot 
be distinguished from these, and may possibly be immature 
males which have not yet acquired the hook to the tentacle ; 
but all the rest can readily be distinguished from those classed 
as males. Itis to be expected that individuals of one sex 
partaking of the characters of the other will occasionally occur, 
just as in the human species feminine men and masculine 
women, and in crustacea female crabs with male tails, are 
met with; and in such cases it may be difficult, if not im- 
possible, for a conchologist to decide upon the evidence of the 
‘shell alone to which sex a specimen belongs. 
The knowledge of this fact in the natural history of Palu- 
dina may prove useful to conchologists engaged in working 
out the fauna of regions or of rocks, such as the Intertrappean 
beds of the Deccan, in which the genus abounds; but it is 
far from probable that any other Gasteropodous genera will 
be found to present similar sexual differences, the large and 
swollen shell of females in Paludina being in obvious correla- 
tion with the viviparous habits universal in the genus but 
unknown in other Gasteropoda, being, in fact, necessitated 
by the great bulk gradually attained by the uterus as the eggs 
develop within it into hard-shelled young Paludine. 
In the European Paludina vivipara a distinct penis is pre- 
sent, and, according to Owen*, “is closely connected with 
the right tentacle ;” but in the Indian species the penis is 
altogether aborted, and its function has been transferred to the 
contiguous right tentacle, which has consequently become 
converted into a hooked copulatory organ. Analogous to this 
is the case of the Dibranchiate Cephalopoda, in which one or 
other of the arms, according to the genus, functions as a penis 
* ‘Lectures on the Comparative Anatomy and Physiology of the 
Invertebrate Animals,’ 2nd ed. 1855, p. 564. 
