F. A. Potts 
53 
their classical experiments on the influence of extracts of foetus on the 
onset of lactation in sheep. 
II. Parasitism and Caste-Formation in Insects. 
In Grassi’s description of the life-history of Termites (1893, 1896) 
we find a curious instance of “ castration parasitaire ” as an apparently 
normal condition in insect individuals. Termite colonies, as is well 
known, contain royal, worker and soldier adults all derived from the 
same kind of egg. Two kinds of larvae may be early distinguished, 
small-headed and large-headed respectively : while the latter produces 
workers and soldiers the former is the material from which the royal 
stock is replenished. The workers and soldiers are (in contrast to the 
Bee, whose workers are all female) of both sexes, but though the 
gonads are present they are of small size. By far the largest part of 
the abdominal cavity is occupied by a coecum of the intestine, whose 
excessive development appears to prevent the development of the 
gonads. The distension of the coecum is due to the presence of 
enormous numbers of parasitic protozoa. These organisms are absent 
in young larvae and in the fully developed sexual forms, but in those 
individuals, the soldiers and workers, whose relief from repi’oductive 
functions is apparently a necessary condition of their usefulness, the 
parasites occasion sterility. It is uncertain exactly how the repression 
of the gonads is brought about, but from the account it seems that 
the great size of the coecum leaves no room for the growth of the 
gonad so that the effect is a purely mechanical one. Though the cause 
is similar the mode of action differs greatly from that in the cases 
in the Crustacea discussed above. The root system of Sacculina and 
Peltogaster practically never comes into contact with the reproductive 
organs—the parasite must act on them indirectly. 
This interesting piece of work shows not only the connection 
between parasitism and sterility but indicates how the termites control 
the appearance of sexually mature forms through diet-regulation. 
The principal food of the termites is wood, often rendered more 
nutritive by passage through the alimentary canal of another indi¬ 
vidual. But in certain cases, namely, the youngest larvae and those 
which are being transformed into sexual forms, the diet is the saliva 
of the workers, and since the recipients of this alone have no gut- 
parasites, Grassi concludes that the saliva is capable of destroying the 
protozoan fauna of the intestine. Should the royal pair come to an 
