1919] McCulloch: Life Cycle of Crithidia and Trypanosoma 137 



monas and Herpetomonas. Leptomonas is a flagellate having the non- 

 flagellated and herpetomonad form in its life cycle ; Herpetomonas 

 has these two stages, together with a crithidial and a trypaniform 

 stage. But such a distinction has not been generally accepted. His 

 chief reason for placing Herpetomonas next to Trypanosoma is the 

 presence of a trypaniform phase in the life cycle of a few herpeto- 

 monad flagellates, as, for example, those found in Musca domestica 

 and Drosophila confusa (Chatton and Leger, 1911). 



From the viewpoint of the present study of these flagellates the 

 hemipteran insect hosts have been frequently divided, for convenience, 

 into the plant-feeding and the blood-sucking types. According to 

 Patton and Cragg (1913) some species of the three families of plant- 

 feeding Hemiptera, the Pentatomidae, the Lygaeidae, and the Coreidae 

 have been found to serve as hosts for either crithidial or herpetomonad 

 flagellates. One more family should now be added to this list, namely, 

 the Pyrrhocoridae, to which the " lupine bug" (Euryophthalmus con- 

 vivus) belongs. Among the blood-sucking Hemiptera some species of 

 the family Reduviidae and the family Cimicidae are parasitized by 

 haemoflagellates having a cycle in a vertebrate host and in some cases 

 by other flagellates having only the invertebrate or insect host. 

 Among the hosts discovered in the family Reduviidae we find Tria- 

 toma (== Conorhinus) megista Burm., the invertebrate host of Schizo- 

 trypanum cruzi (Chagas, 1909) and Triatoma protracta Uhler, the 

 invertebrate host for Trypanosoma triatomae (Kofoid and McCulloch, 

 1916). 



In addition to the hemipteran insects the Diptera (flies, sheep 

 ticks, Siphonaptera (fleas), and Anapleura (lice) also serve as hosts 

 for some of the herpetomonad, crithidial, and trypaniform flagellates, 

 the rat-flea (Ceratophyllus fasciatus) is one of the invertebrate hosts 

 of Trypanosoma lewisi. Frequent reference will be made to this 

 flagellate in the comparison of Crithidia with Trypanosoma. 



The methods of infection of the above hosts have been described 

 as casual, "cross," and hereditary. Of these three methods Patton 

 (1908) proved that nymphs of Lygaeus militaris became infected by 

 ingesting with their food the feces of infected adults. The feces con- 

 tained encysted or spore forms. Porter (1910) described two addi- 

 tional methods for the infection of sheep ticks, the "cross," and the 

 hereditary. The former occurs among insects with cannibalistic 

 habits, the contents and parasites of the digestive tract of one host 

 individual being eaten by another. The hereditary infection has been 



