!9 19 ] McCulloch: Life Cycle of Crithidia and Trypanosoma 139 



sucking bugs, Triatoma protracta Uhler, infected with Trypanosoma 

 triatomae (Kofoid and McCulloch, 1916). 



it is the purpose of the present paper to compare the structure 

 and life cycle in the Crithidia of a plant-feeding bug with the crithidial 

 stages of Trypanosoma in the invertebrate host. In this comparison 

 I shall use as a basis Crithidia euryophthahni, parasitic in Euryoph- 

 thalmus convivus, and the crithidial stages of Trypanosoma lewuii 

 found in Ceratophyllus fasciatus, the account of which as given by 

 Minchin and Thomson (1915) is the most complete of its kind. It is 

 desired to emphasize at this point that our knowledge of the whole of 

 the life cycle of Crithidia in any one insect host is meager as compared 

 with the knowledge gained from the vast amount of time and energy 

 which has been devoted to the study of the invertebrate cycle of Try- 

 panosoma lewisi in the rat-flea. However, C. euryophthalmi for 

 some stages has proved to be the most valuable material for study, and 

 has added materially to our knowledge of the life cycle of these para- 

 sites ; for instance, numerous stages of an endogenous budding process 

 have been found in preparations of this flagellate. 



In addition to considering the comparative morphology and life 

 history of these two flagellates, comparison will be made with C. lepto- 

 coridis (McCulloch, 1915) and with Crithidia. as studied by previous 

 investigators. Schizotrypanum cruzi (Chagas, 1909) and Trypano- 

 soma triatomae (Kofoid and McCulloch, 1916) will also be discussed. 



This work has been carried on under the direction of Dr. C. A. 

 Kofoid, to whom I am indebted not only for his personal interest in 

 the progress of the work but also for advice and helpful criticism. 



HISTORICAL SUMMARY 



In 1915 Minchin and Thompson published the results of their long 

 and careful investigation on the life history of one of these flagellates, 

 the rat-trypanosome, Trypanosoma lewisi, in its relation to the rat- 

 flea, Ceratophyllus fasciatus. These authors stated that their pur- 

 pose in the investigation was to work out the life history and mode 

 of transmission of a trypanosome (in its relation to an invertebrate 

 host) as fully as possible, in order to give us a standard with which 

 the life histories of other species of trypanosomes might be compared 

 as they become known. They selected the rat-trypanosome, Trypano- 

 soma lewisi, a haemoflagellate unable to live in human blood and non- 



