PROTOZOA AND OTHER ANIMALS 963 



gut. Very widespread in wood-eating insects, but by no means restricted 

 to hosts of that group, are the intracellular symbionts studied intensively 

 by Buchner and his associates, as well as by many others (see Buchner, 

 1930). These bacteria or yeast-like fungi live with their hosts in "cyclic 

 endosymbiosis," being regularly transmitted to the next generation. 

 Cyclic endosymbionts exist in the termite Mastotermes (Jucci, 1932; 

 Koch, 1938a, 1938b) . Buchner believed that these symbionts might play 

 a role in the digestive processes of the host, but this opinion, lacking 

 experimental proof, has not been generally adopted (Mansour and 

 Mansour-Bek, 1934b; Schwartz, 1935). 



Protozoa are present in many of these insects, and sometimes them- 

 selves derive nutriment from cellulose-rich materials. Beetle larvae fre- 

 quently harbor a moderate number of small flagellates {Polymastix, 

 Monocercomonoides) which feed on bacteria (Wiedemann, 1930). As 

 stated above (p. 916), a limited number of small, non-xylophagous 

 flagellates (mainly Trichomonas) and occasionally Nyctotherus are pres- 

 ent in many termites of the family Termitidae (Kirby, 1932b, 1937). 

 Some of these higher termites, especially species of Mirotermes and 

 Cuhitermes, harbor large amoebae which ingest wood or other cellulose- 

 rich material on which the termite feeds (Kirby, 1927; Henderson, 

 MS). The wood-feeding roach Panesthia javanica contains two small 

 flagellates, Monocercomonoides and Hexamita; large xylophagous 

 amoebae; smaller amoebae; and a number of ciliates (Kidder, 1937). 

 Mutualistic symbiosis, however, finds its best illustration, so far as 

 Protozoa are concerned, in the abundant and diverse xylophagous flagel- 

 lates of termites other than Termitidae and of Cryptocercus punctulatus. 



According to some investigators, Protozoa and other organisms of 

 the gut may serve the host as a supplementary food source. Wiedemann's 

 observation of cellulose-decomposing bacteria in lamellicorn larvae was 

 mentioned above. He believed that the breakdown products are en- 

 tirely used in the metabolism of other bacteria. The bacteria multiply 

 rapidly in the large intestine, where they live in association with the 

 small flagellates. The mid-gut, he found, secretes protease which is in- 

 active in the alkaline medium there, but in the hind-gut, where bac- 

 terial acids accumulate, it digests the bacteria and flagellates. Mansour 

 and Mansour-Bek (1934a, 1934b) and Mansour (1936) have dis- 

 cussed the possibility that the flagellates in termites do not benefit the 



