312 THE PROTOZOA 



forms with a single nucleus, which is in some cases the tropho- 

 nucleus, in others the kinetonucleus. 



The accounts given of the process of division are somewhat conflicting. 

 According to Martin, division of T. congeri is initiated by the division of the 

 single basal granule of the flagella, followed by splitting of each flagellum 

 longitudinally. Next the trophonucleus divides amitotically, the karyosome 

 becoming first drawn out into a band, after which the nucleus as a whole is 

 constricted into two. Lastly the kinetonucleus becomes elongated, and 

 divides simply by a transverse constriction into two pieces. Jollos, however, 

 following Rosenbusch's statements for trypanosomes, affirms that the division 

 of both nuclei is mitotic in T. helicis. Alexeieff, on the other hand, denies 

 that the kinetonucleus of Trypanoplasnta is a nucleus at all. This author also 

 describes a series of chromatinic blocks at the base of the undulating membrane 

 of T. intestinalis, similar to those seen in Trichomonas (compare Fig. 5). 



Keysselitz (454) has described syngamy in the development of T. " borrdi ' 

 in the leech Piscicola, but the description and figures are unconvincing, and the 

 matter requires reinvestigation. No other investigators have found sexual 

 processes of any kind in trypanoplasms. 



III. THE GENUS CRITHTDIA. 



The distinctive structural feature of Crithidia (Fig. 135, A) is 

 the relatively short undulating membrane wMch, with the single 

 flagellum, arises in the middle of the body from the vicinity of a 



kinetonucleus situated beside, or in front of, 

 the trophonucleus. The form of the body varies 

 from a relatively long, slender type to the short, 

 " barley-grain ' form from which the name of 

 the genus is derived. 



As already pointed out, the application of 

 the name Crithidia as the denomination of a 

 genus is involved in considerable confusion 

 and perplexity partly because the distinctive 

 morphological characters shade off by imper- 

 ceptible gradations into those of trypanosoroes 

 on the one hand, and leptomonads on the other, 



Fio. .135, Crithidia ^ ut stil j more because a certain number of the 

 wmmta,Leger,from . 



the gut of Tabanus species of Crithidia are unquestionably ae- 



tergestinus. A, Or- velopmental stages either of trypanosomes or 

 dinary motile indi- , . , . ' ti , -, 



vidual; B, C, young leptomonads, and others are justly suspected 



forms, with flagel- of being so. In the present state of know- 

 lum short or nidi- -i t i j_ 



mentary. After l ed g e > jt 1S safest to presume that any 



Leger. " Crithidia ' from the digestive tract of a 



blood-sucking insect is a stage of a trypano- 

 some from the blood of a vertebrate, until the contrary has been 

 clearly established. At the same time the possibility must always 

 be taken into account that a blood-sucking invertebrate may 

 harbour flagellate parasites peculiar to itself in addition to those 



