4IO THE BIOLOGY OF INSECTS 



of much interest recently established by the researches 

 of L. Buscalioni and S. Comes (1910), and A. D. Imms 

 (19 19), is that many of the flagellate protozoa living in 

 the intestines of termites (Fig. 84, d) are not parasites but 

 symbionts, obtaining food for themselves and digesting it 

 for the benefit also of the w^ood-eating insects which harbour 

 them. It is only among termites of wood-eating habits 

 that these protozoa abound ; the wood, broken up by the 

 mandibles and gizzard of a termite ''is in a condition of 

 minute fragments and particles," when it reaches the liind- 

 gut, where, as Imms observes, " it gradually becomes taken 

 up and absorbed by the numerous intestinal protozoa." 

 There it undergoes digestion, and " when ejected from 

 the bodies of the Protozoa much of it is . . . capable of 

 being assimilated as food by the host termite." This 

 " pre-digested " nourishment appears to be passed for- 

 ward from the hind-gut into the termite's stomach for 

 absorption. 



Many of the Protozoa that live in insects are, like the 

 tape-w^orms and threadworms already mentioned in this 

 chapter, parasites which in the course of their life-cycles 

 pass to and fro between insect and vertebrate hosts. This 

 twofold relation of insects to other organisms has been the 

 subject of numerous investigations during the last thirty 

 years, and many of the ascertained facts are of high interest 

 and great practical importance. Early in the last century 

 European settlers in Africa found that imported cattle and 

 other domestic animals bitten by Tsetse-flies (Glossina), a 

 blood-sucking section of the muscoid group, were attacked 

 by a fatal disease. David Livingstone's observations on 

 this subject during his journey of 1850-52 are of much 

 interest. After describing the distressing symptoms dis- 

 played by oxen and horses after being bitten by the Tsetse, 

 he remarked that they " seem to indicate a poison . . . the 

 germ of which enters when the proboscis is inserted 

 to draw blood. The poison-germ . . . seems capable, 

 although very minute in quantity, of reproducing itself." 

 One cannot be certain that writing thus of a " very minute 



