22O L. R. CLEVELAND. 



on microorganisms." However, microorganisms are not asso- 

 ciated with these insects as symbionts certainly not in the same 

 sense or degree that termite protozoa are associated with their 

 host but as food. 



The nitrogen content of birch-wood is very high as compared 

 with that of other woods. It is 0.108 per cent. In many woods it 

 runs as low as 0.08 per cent. From the work of Baumberger 

 (1919) and others, it is evident that many insects, due to the low 

 protein content of the substratum on which they live and feed, 

 are dependent on microorganisms for the proteins which they 

 contain. Since such a small amount of protein is present in the 

 food of termites it is quite likely that they, too, are dependent on 

 microorganisms for a part of their proteins. Fungi may often be 

 seen in the intestine of many termites. 



The relation of ambrosia beetles to fungi has been studied by 

 Hedgcock (1906) and others, and the fungus-growing habits of 

 the Termitidse have been studied by many investigators, chief 

 of which are Doflein (1905 and 1906), Fetch (1906) and Escherich 

 (1909), but the exact relation of these insects to the fungi is not 

 known. The fungi may simply furnish food (protein) for the 

 insects, and, on the other hand, they may elaborate substances 

 from the wood and grasses which the beetles and termites can- 

 not elaborate, which substances are very important in the in- 

 sects' metabolism. 



Internal symbionts (yeasts) have been described from the 

 beetle Anobium panicetim, by Karawaiew (1899) and Escherich 

 (1900), and Portier (1905) claims that a micrococcus and a fungus 

 live symbiotically with the caterpillar Nepliliica, but in no in- 

 stance have intestinal flagellates been shown to live symbioti- 

 cally with their host. The flagellates living in termites are the 

 first example of such a relationship. 



As a rule the second and third reproductive forms do not 

 harbor intestinal protozoa. Why? For one of two reasons per- 

 haps: (i) the liquid diet upon which these individuals are fed 

 kills the protozoa; (2) the failure of the host to eat wood causes 

 the death of the protozoa. There is more evidence in favor of 

 the latter view. In the first form reproductive adults protozoa 

 are usually present though never in abundance as in workers 

 and soldiers and this form eats some, though never as much 



