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. helicia. Alexeieff, on the other hand, denies 

 that the kinetonucleus of Trypanoplasma 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 Pig. 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 CRITHIDIA. 



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

 the relatively short undulating membrane which, 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 trypanosomes 

 on the one hand, and leptomonads on the other, 

 but still more because a certain number of the 

 " species of Crithidia " are unquestionably de- 

 velopmental stages either of trypanosomes or 

 leptomonads, and others are justly suspected 

 of being so. In the present state of know- 

 ledge, it is safest to presume that any 

 " 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 



VL 



FIQ. 135, Crithidia 

 minuta, L6ger, from 

 the gut of Tabanua 

 tergestinua. A, Or- 

 dinary motile indi- 

 vidual; B, G, young 

 forme, with flagel- 

 lum short or rudi- 

 mentary. After 

 Leger. 



