358 FAMILY: TRYPANOSOMID^ 



by their flagellar ends, or attached to cells or debris (Fig. 166, 9). Multi- 

 plication of these forms again takes place. 



Flagellates of all sizes and shapes are found not only in the crop, but also 

 in the other parts of the intestinal tract. In the rectum there is a gradual 

 production of short forms, by a process the reverse of that which occurred 

 in the crops of the nymphs, by the drawing in of the anterior and posterior 

 ends (Fig. 166, 21-26). Oval or round forms measuring 4 to 6 microns 

 by 3 to 4 microns are thus produced. The flagellum is lost or absorbed, 

 the axoneme alone remaining. These forms become enclosed in cysts of 

 various sizes. Not only are these cysts voided with the faeces of the bug, 

 but any other forms which may be present in the rectum also escape, 

 so that it is possible the nymphs may become infected, not only by ingestion 

 of the cysts, but of the unencysted forms also. Patton has noted that 

 the bugs have cannibalistic habits, and often kill and feed on one another, 

 so that infection may take place in this manner. The flagellates were 

 never found in any other organ than the intestine, and there was no 

 evidence that infection of offspring through the eggs could take place. 



The life-history of Crithidia gerridis is very similar to that of Lepto- 

 monas ctenocephali, there being direct infection from host to host by 

 means of cysts voided in the faeces. The difference is that the flagellates 

 develop further towards the trypanosome type. Becker (1923, 19236), 

 in a study of C. gerridis in Gerris remiges in North America, actually 

 noted that trypanosome forms occasionally appear. He has also seen the 

 flagellate in Microvelia americana, G. marginatus, and G. rufoscutellatus. 



Fantham and Porter (1916) stated that they had infected vertebrates 

 by inoculating them with C. gerridis. Becker (1923«) has failed entirely 

 to confirm these observations. 



A cycle of development similar to that of C. gerridis has been described 

 by Patton (1909) for C. tahani of Tahanus hilarius and Tahanus sp., and 

 by Porter (1911) for a parasite of the human flea, Pulex irritans. The 

 latter flagellate was given the name C. pidicis, which had previously been 

 used by Balfour (1909a) for a similar, though not necessarily identical, 

 form discovered by him (1906a) in the flea, Loemopsylla cleopatrce, in the 

 Sudan. From the observations of Noller (1916), it seems probable that 

 the Crithidia of tabanid flies are really developmental stages of Trypano- 

 soma theileri (see p. 501). 



Crithidia hyalommae O'Farrell, 1913. — This flagellate is worthy of 

 special consideration, not only because it infects the body cavity fluid 

 of its host, Hyalomma cegyptium, but also because actual infection of the 

 ova is described as leading to infection of the hatched offspring (Fig. 167). 



The parasite was found by O'Farrell in ticks living on cattle in the 

 Anglo-Egyptian Sudan. In the first place, it might be suggested that 



