242 



THE PATHOGENIC FLAGELLATES 



withdrawal of the flagelltim. This gradually shortens and disappears, a 

 rhizoblast remaining for some time; but this too is ultimately absorbed, 

 and as a "gregarine" form the minute organism makes its way to 

 epithelial cells, where it becomes attached (Fig. 93). 



Since Leger's original observations several others have worked upon 

 different species of crithidia, the most recent results being obtained by 

 Patton ('08) in connection with a species (Cr. gerridis, Patton) from 

 a water bug, Gerris fossarum, and by Flu ('08) in connection with a 

 species (Cr. melophagia, Flu) from Melophagus ovinus, an ectoparasite 

 of sheep. In each of these there are well-defined, non-flagellated con- 

 ditions of the organisms similar to those of H. donovani. A nucleus 

 and blepharoplast are present, and the flagellum develops from the 

 latter by the apparent outgrowth of its substance (Fig. 95). In 



Stages in the development of Crithidia gerridis, Patton. (After Patton.) A, group of 

 young forms from mid-gut of nymph of Gerris fossarum, Fabr.; blepharoplast and origin of 

 flagellum; B, development of the flagellum inside the periphery of parasite; C, further develop- 

 ment and division of flagellum; D, E, adult forms, flagellum dividing in E; F, two stages in 

 withdrawal of flagellum to form resting stages; G, cyst. 



Cr. gerridis the flagellum forms as a ridge upon the surface, and often 

 divides as it grows, the basal bodies first dividing into two. By con- 

 tinued division rosettes of many individuals may be formed before 

 the fully developed flagellated adults break away. Division occurs as 

 in herpetomonas (Fig. 96). 



Encysted forms similar to those described by Prowazek for her- 

 petomonas were observed by Flu in the case of Cr. melophagia, but 

 not in Cr. gerridis. Cr. melophagia further differs from other forms in 

 possessing definite myonemes which run the length of the body, unit- 

 ing in the anterior end with the rhizoblast of the flagellum (Fig. 95). 



