138 University of California Publications in Zoology [Vol. 19 



described for Melophagus ovinus (Porter, 1910). The erithidial flag- 

 ellates penetrate the wall of the digestive tract, make their way into 

 the ova, and thus infect, the next generation. Infection among the 

 blood-sucking insects is usually due to the taking in of infected blood 

 from the vertebrate host. 



Closely associated with the habits of these hosts in securing their 

 food are the variations in the structure and life cycles of the infecting 

 flagellates. In general it may be stated that the haemoflagellates, i.e., 

 trypanosomes, liave two hosts in their life-cycle, an invertebrate and 

 a vertebrate, while "natural," or leptomonad, herpetomonad, and 

 erithidial flagellates are thought to have normally only the invertebrate 

 host. Blood-sucking hosts can be infected with both types of flagel- 

 lates, the so-called natural flagellates and the haemoflagellates. or try- 

 panosomes. Plant-feeding hosts, so far as known, are infected with 

 the natural flagellates only. Patton (1909) came to the conclusion 

 that all the erithidial stages found in the insect host are natural para- 

 sites and that the blood parasites, trypanosomes, undergo no develop- 

 mental process in the invertebrate host. On the contrary, the work 

 of Minchin and Thomson (1915) on Trypanosoma lewisi, which is the 

 most conclusive that has been done, clearly proves that this haemo- 

 flagellate at least does pass through a definite life-cycle in the digestive 

 tract of the flea. 



Another interesting feature of the natural flagellates is brought 

 out in the recent work of Fantham and Porter (1915a, b, c). They 

 conclude that intestinal flagellates of insects such as Herpetomonas 

 pattoni, a natural flagellate of the intestine of the flea, can adapt 

 themselves to life in the blood of mice. These investigators have also 

 proved that other intestinal flagellates from insects, such as Herpe- 

 tomonas jaculum, H. stratiomyiac, H. pediculi, and Crithidia g> rridis 

 become pathogenic to mammals when the latter have been fed on, 

 or inoculated subcutaneously or intraperitioneally with them. Herpe- 

 tomonas jaculum and Crithidia gerridis have also been successfully 

 fed or inoculated into cold-blooded hosts, namely, fishes, frogs, toads, 

 lizards, and grass snakes, according to the above investigators. 



My work with flagellates of the hemipteran insects has been con- 

 fined to a study of the erithidial flagellates of two supposedly plant- 

 feeding insects, the box elder bug, Leptocoris trivittatus Hahn, para- 

 sitized by the flagellate Crithidia leptocoridis (McCulloch, 1915), and 

 the lupine bug, Euryophthalmus convivus Stal, containing Crithidia 

 euryophthalmi (McCulloch, 1917), and flagellates of one of the blood- 



