Sex determination.

Guido Bacci

Date:: [1965]

Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Sex determination. Source: Wellcome Collection.

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SEX PHENOTYPES IN HERMAPHRODITISM 149 trocophora and swim around the rocky bottom where the parents live (Fig. 7.10). Baltzer showed (1914-1937) that, if the larvae settle on the proboscis of a ripe female, they develop into males, if on the contrary they settle far from the adult female individuals they differentiate into females. If the larvae that have settled on the proboscis are removed after a short period and they are compelled to develop in pure sea water, intersexes are obtained. Their male characters will appear the more marked the longer the permanence upon the female body. Isolated larvae, which are kept in an aquarium, generally develop into females but if pieces of a proboscis are put in the aquarium the larvae are developed into males. The same male producing action is obtained by employing water extracts of the proboscis and of the intestine (Baltzer, 1926; Nowinski, 1934). A high percentage of male individuals was also obtained from free living larvae with the addition of inorganic substances to the pure sea water of the cultures (Herbst, 1928-1936). Addition of CO2, of HCl, of K+ and traces of Си + + produced from 60 per cent to 92 per cent male individuals. Also the subtraction of SO4, and of Mg + + ions from the sea water induced the differentiation of about 90 per cent Bonellia larvae into males. Sex determination appears thus to be purely phenotypical to various authors (Goldschmidt, 1931; Hartmann, 1937) but Baltzer (1932) pointed to the remarkable fact that a few Bonellia larvae differentiate as males also in the absence of ripe females and of their extracts and on the other hand some larvae do not attach themselves to the female proboscis when present and therefore they develop as females. The situation of these male and female larvae seems therefore to be very similar to that of pure males and females in the Patella case (Bacci, 1947b). The peculiar example of sex determination in Bonellia, which assures the production of two stable sexual states in the absence of a sex chromosome mechanism, provides an excellent example of sexual adaptation to the peculiar condition of a sessile animal. The sex determination in parasitic animals, which so far has been only tentatively explored, provides an impressive example of sexual adaptation. Sex and Parasitism 1. lone thoracica lone thoracica is a species of isopod which lives as a parasite on the gills of Callianassa laticauda, a decapod crustacean. Reverberi and Pitotti (1942) demonstrated that the isopod reaches the gills of the host in the sexually undifferentiated stage of copepodite larva. The first larva that reaches the gill of Callianassa always develops as a female and the second larva differentiates into a dwarf male that lives attached to the female body (Fig. 7.7). Evidence