Some Phenomena associated with Parasitism

Abstract

(1) The marked peculiarity in infection of Decapod Crustacea by certain parasites is the alteration of the sexual characters of the hosts (castration parasitaire of Giard). This has a twofold nature, viz.:—(a) Sterility. In both sexes gonads dwindle and may entirely abort.(b) Assumption of characters of other sex. In the male the external characters proper to the female are assumed in greater or less degree. The testis is transformed into a hermaphrodite gland, either while still infected by the parasite (incipient hermaphroditism of hermit crabs) or when freed from its influence (ripe ovotestis in spider crab). The reverse effects are not found in the female.(2) This phenomenon occurs throughout the Invertebrata, but though sterility is a frequent consequence, the alteration of sex characters is never so definite as in the Crustacea. Analogous observations on parasitism in the Vertebrata have not been made.(3) In the Insecta, parasitism appears to influence caste production. Grassi suggested that the sterility of soldiers and workers in Termites is due to protozoan parasites. In ants a giant caste is known (mermithergates) always harbouring a nematode worm.