314 



THE PROTOZOA 



The distinctive structural features of this genus are the possession 

 of a single flagellum, arising from close beside a kinetonucleus 

 which is placed far forwards in the body, and the entire absence 

 of an undulating membrane (Fig. 136, B ; Fig. 137, d). As already 

 stated above, however, the application of the names Leptomonas 

 and Herpetomonas is much disputed, and the morphological defini- 

 tion of the genera in question is attended with considerable diffi- 

 culties, chiefly owing to the fact that in one and the same host a 

 great variety of forms may occur, with regard to which it is not 

 possible, in the present condition of knowledge, to state with cer- 

 tainty whether they represent distinct species of flagellates, refer- 

 able even to distinct genera, occurring fortuitously in the same 

 host, or whether they are all merely developmental phases of the 

 same species. The following are the principal forms which may 



F G 



FIG. 136. Leptomonas jaculum, Leger, from the intestine of Nepa cinerea. A, B, 

 Monad forms ; G, division of a monad form ; D, monad form with short 

 flagellum ; E, F, G, gregarine-like forms : E, in division, F. attached to an 

 epithelial cell by the rudimentary flagella, which resemble the rostra of gre- 

 garine sporozoites. After Leger. 



occur together in the same host : (1) Large, biflagellate individuals 

 (Fig. 124, A), often with a distinct pair of rhizoplasts connected 

 with the two flagella, the type to which, according to one set of 

 opinions, the name Herpetomonas should be restricted, but which 

 on another view represents merely an early stage in binary fission, 

 with a daughter- flagellum precociously formed.; (2) smaller flagel- 

 lates with a single flagellum (Fig. 136, B ; Fig. 137, d), the type for 

 which the name Leptomonas is employed by those who regard the 

 true Herpetomonas as typically biflagellate, while by those who hold 

 the contrary view the two genera are ranked as synonyms ; (3) cri- 

 thidial forms (Fig. 137, g) ; (4) trypaniform flagellates (Fig. 137, j. k}, 

 with the kinetonucleus at the posterior end, and the flagellum 

 running the whole length of the body with a more or less distinct 

 undulating membrane the " leptotrypanosoines " of Chatton. In 



