ABSTRACT
Contrary to the assertion of Giard that Leander males when parasitized by Bopyrus undergo sex reversal, Leander xiphias and L. squilla show no modifications of the secondary sex characters, while the testes, although reduced in size, never produce oocytes. This is probably true also of L. serratus.
The power of a parasite to induce sex reversal is probably limited by the degree of sex separation of the host species. The species which show sex reversal (“castration parasitaire”) are thus considered to possess a less complete sexseparating mechanism than those, such as Leander, which are not reversed by parasites.
Breeding females of Leander develop an incubatory chamber under the abdomen, involving many structural changes.
These “breeding characters” are not formed by parasitized females, nor by females castrated by X-rays.
It is possible that there is a female sex hormone in Crustacea, but the evidence is not yet conclusive.
The correlation tables used in the construction of the graphs have been deposited at the British Museum.
By the kindness of the authorities at the British Museum and at the Marine Biological Laboratory, Plymouth, I have been able to examine a few further species of prawns carrying Epicarid parasites, (a) Leander serratus (Pennant), Epicarid Bopyrus squillarum Latreüle. Out of about eighty specimens, thirty were males and in no case was there any sign of sex reversal. (b) Bandolina brevirostris (Rathke), Epicarid Pleurocrypta cluthae T. Scott. Out of seven specimens, two were males showing no signs of sex reversal, (c) Nineteen specimens of Processa canaliadata Leach = Nika edulis Risso, Hippolyte spp. and Spirontocaris spp. parasitized by Phryxus spp. or Bopyrus spp., were all females. In no case was there any trace of the copulatory style, and thus it seems unlikely that any were sex-reversed males. However, the fact of not finding a single male in this material is puzzling.
This is not the case in Pandalina brevirostris, where I have sedh a parasitized female carrying a few eggs in the incubatory chamber. If the parasite dies, females of Leander serratus can recover completely and bear a full complement of eggs in the incubatory chamber.
A further character developed by the breeding females of Leander consists of large numbers of white chromatophores around the incubatory chamber (see Knowles & Callan, 1940).
