THE GENERA HERPETOMONAS AND CRITHIDIA 



241 



Patton finds no evidence of encystment and no evidence of infection 

 of the bedbugs otlier than from human victims. Nor is there any 

 evidence to support the idea of direct inheritance from female bugs to 

 their offspring, but Patton suggests in a later paper (1908) that nymphs 

 of blood-sucking forms of such bugs may take in the infection with 

 their food. The method of reentry into a human host is likewise 

 unknown. 



B. The Genus Crithidia, Leger, 1902. — The genus crithidia, by 

 reason of its non-kinetic prolongation of protoplasm at the base of the 

 flagellum, forms an interesting link in the evolution of the trypano- 

 somes. It is Cjuite true, as Novy, MacNeal, and Torrey ('07) point 

 out, that the distinctions between these several genera are extremely 

 "fragile," and that the points of difference are so minute as not to 



Fig. 95 



Crithidia melophagia, Flu, from the gut of Melophagus ovinus. (After Flu.) A, fully 

 developed parasite with myonenies; B, individual with degenerated trophonucleus; C, 

 encysted fonii (see herpetomonas) ; D, division form. 



count for much. It must not be overlooked, however, that minute 

 differences must be utilized in connection with organisms that are 

 themselves minute, and a definite structural feature which Liihe 

 points out as the most characteristic of the genus crithidia, since it 

 exists in all of the parasites regardless of their size, is a perfectly 

 satisfactory differential characteristic, and unlike Leger's original 

 basis of distinction (smaller size of crithidia and truncated ends), 

 has morphological value. 



The type species is Crithidia subulata, Leger, a parasite of the 



intestinal tract of a tabanid fly. The body is elongate and slender and 



drawn out upon the base of the flagellum in a typical manner (Fig. 93, 



p. 235). The nucleus and blepharoplast are distinct and persistent after 



16 



