CHAPTER XXVIII 

 THE INTESTINAL FLAGELLATES OF INSECTS 



By 



Elery R. Becker 

 Iowa State College 



The numerous species which constitute the flagellate fauna of 

 insects' intestines may be separated, for the sake of convenience, 

 into four general groups. 



First, there are the forms, many of them complex and rather 

 bizarre, some of them cellulose-digesters, which live in the intes- 

 tines of certain families of termites. One genus, Lophomonas, 

 which shows close relationships with certain of the termite flagel- 

 lates is found in roaches. Since the termite protozoa are treated 

 in Chapter V, they will be entirely omitted from the present one. 



Secondly, there are flagellates belonging to the family trypan- 

 OSOMID.E (Doflein) which spend a part of their life-cycle in the 

 intestines of insects and the remainder in the blood stream or 

 tissues of vertebrates. In such cases the insect is referred to as 

 the intermediate host, but we must remember that in the natural 

 order of things the flagellate is as much a parasite of the insect as 

 of the vertebrate. In fact, there is abundant ground for believing 

 that such flagellates have evolved from exclusively insect types. 

 It is not inconceivable that some of the forms which we regard 

 to-day as belonging to the genera Herpetomonas and Crithidia may 

 in reality be phases in the insect of flagellates which have also a 

 definitive vertebrate host. As an instance of this kind we could 

 cite the case of the flagellate of the sheep ked which was supposed 

 by many to be a Crithidia until Hoare (1923) showed experi- 

 mentally that it was in reality Trypanosoma mclopJiagimn in its 

 insect intermediate host. Other such cases of this kind should be 

 looked for. What is the insect host, if any, of Trypanosoma ameri- 

 canum said to be common in American cattle? Is Crithidia tabani 



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