TRANSACTIONS OF SECTION D. 543 
MONDAY, AUGUST 5. 
The following Papers were read :— 
1. Sex in the Crustacea, with special reference to the Origin and Nature 
of Hermaphroditism. By Grorrrey Smitu, M.A. 
The great majority of Crustacea have the sexes separate, and this is also true 
of the phylum Arthropoda as a whole. ‘There are, however, two large groups of 
Orustacea, the Cirripedia and the parasitic Isopoda, which are for the most part 
hermaphrodite; and since these two isolated groups stand alone in this respect among 
allied groups, we may be certain that the hermaphroditism has been secondarily 
acquired from some dicecious ancestor. It is therefore interesting to inquire 
under what conditions hermaphroditism may arise in a dicecious species. 
The most searching analysis of hermaphroditism is afforded by the phenomena 
of parasitic castration, which was first discovered by Giard,1 and has been sub- 
sequently studied by the author? and Potts.* The result of these studies has been 
to show that a number of animals belonging to widely diversified phyla, but 
especially the Crustacea, when attacked by various parasites, undergo an alteration 
in their sexual nature of such a kind that at first the gonad in both sexes degene- 
rates to a greater or less extent; secondly, the males assume in varying degrees 
the secondary sexual characters proper to the female, while the female, without 
assuming any male character, suffers a certain amount of degeneration in the 
secondary characters proper to the female. Finally, either on recovery from the 
parasite or else during the degenerative process, the male may develop ova in its 
testes, and these ova may grow to a very large size, lying side by side with mature 
spermatozoa. The females, on the other hand, just as they never develop male 
secondary characters, also never produce spermatozoa in their ovaries. These 
results apply especially to the effects of the parasitic Rhizocephala upon the crabs 
which they infect. 
We see then, first, that hermaphroditism in the Crustacea can be called 
forth in its completion by an external cause acting upon a sexually differentiated 
animal, and secondly, that it can only be called forth in this way in the male sex, 
not in the female. 
What is the nature of this cause? If we look for parallel cases, we find in 
the Crustacea that a partial temporary hermaphroditism is assumed by the males 
of certain forms (especially crayfishes, spider-crabs, and sandhoppers of the 
genus Orchestia) at particular seasons, when a period of growth as opposed to one 
of reproduction is being initiated. It appears that the males, in order to increase 
their vegetative activity, have to suppress the male part of their organisation and 
call into play the female part. This also gives an explanation of the behaviour of 
males under the influence of parasites ; for in order to cope with the drain on the 
system caused by the parasite they have to increase their vegetative activity, and 
this they do by suppressing their male organisations and calling into activity the 
female, which they possess in a latent state. 
These facts point to an extremely close connection between sex and meta- 
bolism in general. 
The conclusion that hermaphroditism is a property of the male sex developed 
in response to altered conditions of metabolism can be applied to the origin and 
nature of the hermaphroditism found normally in the Cirripedes and parasitic 
Isopoda. Both these groups lead a sessile, inactive existence when adult, and in 
them the passive vegetative functions are developed to a high degree. 
In the parasitic Isopoda all the individuals are at first males, when they live 
a larval free swimming existence ; on settling down to the parasitic existence they 
develop the female part of their organisation. The Cirripedes exhibit many 
interesting variations; but the presence in some of them of males which may 
1 Bull. Sc. Dép. Nord, 10, 11. ie * Naples Monograph, Rhizocephala. 
WJ. MWS., vol. 1. 
