1919J McCulloch: Life Cycle of Crithidia and Trypanosoma 143 



question immediately arose as to whether or not all the crithidial infec- 

 tions of these regions are a part of the stomach phase of the life 

 history of C. euryophthalmi. A careful study of the crithidial infec- 

 tion of each of these portions of the digestive tract together with many 

 examinations of the contents of the intestine, the gland, and the 

 rectum, convinced me that food conditions do not permit the parasites 

 to establish a permanent rectal phase in the rectum but that they 

 are forced to remain anterior to the intestine, in the pyloric expansion. 

 Preparations of the gland and intestine have as yet shown no infection 

 posteriorly, and the rectum has contained an occasional infection of 

 spore forms only. 



To add to the difficulty in determining the extent of the stomach 

 phase and the beginning of the rectal phase no structural changes of a 

 striking nature occur in the stomach phase of C. euryophthalmi as is 

 the case in T. lewisi; nevertheless, the behavior of the crithidias is of 

 some assistance and the study of the serial sections and stained smears 

 of the several parts have added materially to our knowledge of the 

 phases. Taking into consideration the evidence from these sources 

 the crithidial infection of the "crop" is interpreted as the stomach 

 phase. The mid-stomach serves as a temporary location for the slowly 

 migrating forms of the stomach phase, and the pyloric expansion be- 

 comes the region of the permanent location of the "rectal" phase 

 during the life of the lupine bug. The established "rectal" phase 

 of the life history, of C. euryophthalmi in the pyloric expansion has 

 three general types of individuals, the attached, or haptomonad, the 

 free, or nectomonad, and the final spore forms, which probably serve 

 to infect another insect. Only the last type of parasite has been found 

 in the normal contents of the rectum. 



With these brief explanatory outlines of the life histories of T. 

 lewisi and of C. euryophthalmi a detailed discussion of the more im- 

 portant points concerning the comparative morphology of the crith- 

 idial stages of Trypanosoma and of Crithidia will now be given. The 

 comparison of the life cycles which follows is based upon the work 

 of Minchin and Thomson on the life cycle of T. lewisi, and upon 

 the life history of C. euryophthalmi with special reference to the 

 accompanying plates (pis. 2-6). For further details of the life 

 history of T. lewisi the reader is referred to Minchin and Thomson's 

 paper (1915). 



