1919] McCuUoch: Life Cycle of Crithidia and Trypanosoma 171 



changes which convert crithidiomorphic forms into crithidias are 

 taking place. 



The frequency with which we find preparations of the "crop" 

 free from infection with C. euryophthalmi, the less frequency of infec- 

 tion of the mid-stomach, together with the almost invariably heavy 

 infection in the pyloric expansion, lead us to the conclusion that the 

 crithidias of Euryophthalnnis convivus have the same tendency to 

 migrate posteriorly as does T. lewisi in the flea. In C. euryophthalmi, 

 however, the movement is less marked than in T. lewisi. This tendency 

 of slow progression posteriorly doubtless depends upon the move- 

 ment of food contents from the "crop" into the mid-stomach and 

 pyloric expansion. 



The migrating mass of crithidias from the "crop" soon establishes 

 three distinct types of parasites in the pyloric expansion : the necto- 

 monads or free flagellates, the haptomonads or attached flagellates, 

 and the infective spores which serve for transmitting C. < uryophthalmi 

 to another host. These types or classes of parasites are comparable in 

 almost every way to the nectomonads, or free flagellates, the hapto- 

 monads, or attached flagellates, and the final trypaniform stage of the 

 rectal phase of T. lewisi. The nectomonads and haptomonads of each 

 life-cycle are almost identical in structure and behavior. 



NECTOMONADS 



Smear preparations of the mid-stomach and of the pyloric expan- 

 sion show little difference in the morphological structure of their 

 crithidial infection. The serial sections of these two parts, however, 

 show a sharp distinction in the structure of haptomonad forms and 

 the nature of the epithelial lining to which they are attached, and 

 a slight distinction in the structure of the nectomonads in the mid- 

 stomach and in the pyloric expansion. The nectomonads of the 

 former are usually of the elongate, slender type (pi. 5, figs. 73-80). 

 The zooids, the result of the processes of multiple fission (pi. 4, 

 figs. 40-54) are abundant in the smear preparations of both regions. 

 The series sections thus far have shown numerous zooids (pi. 4, 

 figs. 40-50) in the anterior portion of the mid-stomach. These 

 zooids (pi. 4, fig. 40) are frequently grouped together in the grooves 

 between epithelial cells. For this reason it is possible that the cur- 

 rent of food in passing down the digestive tract failed to carry 

 them on into the pyloric expansion. The zooids are small forms, 



