F. A. Potts 
55 
the production of small-headed workers only. Another feature of the 
mermithergate is the development of ancient characters which have 
been lost in the soldier, namely ocelli and larger eyes. 
The mermithergate proves that parasitism may stimulate growth 
of the host, and in a footnote to his paper Wheeler quotes Montgomery 
as saying that crickets infected with Mermis are apt to be larger than 
normal individuals. We have shown above that in parasitised hermit 
crabs a similar tendency is found. Possibly a comparison with fowls 
may justly be made where the relief from the processes of reproduction 
which follow caponisation is responsible for the increased size of 
the capons. 
Summary. 
(1) The marked peculiarity in infection of Decapod Crustacea by 
certain parasites is the alteration of the sexual characters of the hosts 
(i 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 observa¬ 
tions on parasitism in the Yertebrata 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. 
BIBLIOGRAPHY. 
Boulenger, C. (1908). On the hermaphroditism of the amphipod Orchestia 
deshayesii Andouin. London Proc. Zool. Soc. pp. 42-47. 
Faxon, W. (1885). Revision of the Cambaridae of America. Mem. Mus. Zool. 
Comp. Harvard , vol. x. 
Giard, A. (1887). La castration parasitaire. Bull. soc. Dep. du Nord, ser. 2, 
vol. x., pp. 1-23. 
