282 



THE PROTOZOA 



Trypanosoma, Crithidia, and Leptomonas, of which Leishmania may 

 be regarded as the resting, non-flagellated phase ; and the bodonid 

 or heteromastigote type with two flagella, seen in Trypanoplasma 

 and Prowazekia. We shall return to this point in considering the 

 affinities of the group as a whole and of its constituent genera. 



The six types enumerated above are given with the nomenclature and 

 definitions most commonly accepted, but it is necessary to state that the 

 application and significance of the names Crithidia, Leptomonas, and Herpeto- 



monas, are much disputed and are far from 

 being settled. The type of the genus Herpeto- 

 monas of Saville Kent is a species found in 

 the digestive tract of house-flies, H. muscce- 

 domesticce (Fig. 124). According to Prowazek 

 (557), this form possesses normally two 

 flagella, which are connected together by a 

 membrane ; according to Patton (551) and 

 many others, the biflagellate condition is due 

 to precocious division of the normally single 

 flagellum as a preparation for division of the 

 body (compare Strickland, 558 ; Wenyon, 84). 

 Those who follow Prowazek in regarding the 

 biflagellate condition of Herpetomonas as its 

 normal adult form employ the older genus 

 Leptomonas of Saville Kent* for forms with a 

 single flagellum (Chatton,Roubaud, Prowazek). 

 The main source of the confusion in the nomen- 

 clature arises from the uncertainty which still 

 exists in many cases as to whether a given form 

 or structural type is to be regarded as an in- 

 dependent specific or generic type, or as a 

 developmental phase of another species. This 

 applies especially to the genus Crithidia, 

 founded by Leger (543) for a species, C. 

 fasciculata, from the intestine of Anopheles 

 maculipennis, and defined as a small uniflagel- 

 late form shaped like a grain of barley (Greek, 

 Kpi6r}). Such forms, however, occur as 

 developmental forms of trypanosomes or of 

 leptomonads, and it is extremely probable that 

 the species on which Leger founded his genus 

 was simply a phase of this kind, which Wood- 

 cock (527) has proposed to call the " trypano- 

 monad" phase, in the development of a 

 trypanosome. On this ground Dunkerly 

 (535), who has recently discussed the whole 

 question, considers that the name Crithidia 

 cannot be used as a generic name at all, but must be merged in Leptomonas, 

 the name that should be used for all the uniflagellate parasites of insect -guts ; 

 while Herpetomonas should either become a synonym of Leptomonas, or should 

 be used solely for Prowazek's biflagellate type, if that prove to be a distinct 

 generic type. On the other hand, Leger and Duboscq (646, p. 232, footnote) 

 consider that Crithidia should be retained, and Leptomonas ranked as a 



* The genus Leptomonas was founded by Saville Kent, <; Manual of Infusoria," 

 vol. i., p. 243, for L. biitschlii, parasite of the nematode worm Trilobus gracilis ; 

 the genus Herpetomonas was founded on p. 245 of the same work for H. muscce- 

 domesticce and H. lewisi ( = Trypanosoma lewisi). Leptomonas is therefore techni- 

 cally the older genus. 



B 



FIG. 124, H erpetomonas 

 muscce-domesticce (Burnett). 

 A, Motile individual with 

 two flagella ; B, cyst : n., 

 nucleus ; bl, kinetonucleus. 

 After Prowazek. 



