964 PROTOZOA AND OTHER ANIMALS 



hosts in nutritive processes except that, multiplying and being digested 

 continually, they are a direct and supplementary food source for the 

 insects. This seems unlikely, however. The flagellates in termites 

 multiply rapidly for a few days after a molt following which there has 

 been a new infection; then there is little division, and they are destroyed, 

 usually, on the approach of the next molt. What use the host might 

 make of the disintegration products at that time is entirely unknown, 

 but certainly there is no evidence that the Protozoa could be available 

 at any other period as a supplementary food source accounting for gen- 

 eral nutrition (see p. 968). 



Cyclic endosymbionts seem to be necessary for normal development 

 of the host in some instances. Aschner and Ries (1933) and Aschner 

 (1932, 1934) succeeded in freeing Pedicuhis of the symbionts that 

 normally inhabit the mycetome, and found that without them larvae 

 died sooner or later. The harmful effects of the absence of symbionts in 

 Pediculus were reduced by rectal injection of yeast extract. Koch ( 1933a, 

 1933b) obtained symbiont-free larvae of the anobiid S'/todrepa pankea 

 and found that they would not develop normally unless yeast was added 

 to the food. (Koch, however, also reported freeing the saw-tooth grain 

 beetle Orzyaephilus surinaniensis of symbionts in the mycetomes by in- 

 cubation [1933b, 1936]; and absence of the microorganisms seemed to 

 be without detrimental efl^ect. ) It has been suggested that the symbionts 

 are sources of vitamins or growth factors. It is possible, in the light of 

 these facts, that certain symbiotic Protozoa may be necessary to the life 

 of the host, without participating in the digestive processes or serving 

 as a food source important in bulk. 



We now come to a consideration of the demonstration — one of the 

 outstanding advances in modern protozoology, though not yet complete 

 — that wood-eating flagellates in termites and Cvyptocevcns are neces- 

 sary for the survival of their hosts in making the products of decomposi- 

 tion of cellulose available for the nutrition of the insects. This has justly 

 received very wide attention, so it is unnecessary to recount all details 

 of the demonstration here (see Cleveland 1924, 1926, 1928a, 1934). 



Termites feed primarily upon wood. This is especially true of the 

 members of the families Mastotermitidae, Kalotermitidae, and Rhino- 

 termitidae. Many Termitidae attack wood also; others bring into their 

 nests dried grass, ingest soil and extract from it the nutrient materials 



