THE GENUS TRYPANOSOMA 259 



female, while Minchin ('08) states, in connection with Tryp. gamblense, 

 that only the extremes remain after twenty-four hours in the diges- 

 tive tract of the fly, thus indicating that such extremes are physiologi- 

 cally adapted to resist unfavorable conditions, while the intermediate 

 forms are killed off. It is intimated that such resistance may be inter- 

 preted as indicating two physiological grades, which may be identified 

 as male and female. This conclusion, however, is weakened by the 

 fact that intermediate forms reappear during the second day. Dof- 

 lein's ('09) criticism that such size differences may represent young 

 and old individuals is certainly to be considered. Moore and Breinl 

 describe very remarkable forms of Tryp. yambiense, in which the 

 kinetonucleus grows out into a long rod reaching to the nucleus. Such 

 forms recall Prowazek's "male" of Tryp. lewisi, but the English 

 observers hold that it indicates the preparation for union of a part of 

 the rod with the nucleus, i. e., a type of autogamy. 



While it is quite obvious that the last word has not yet been written 

 in regard to such trimorphism in trypanosomes, there is no doubt at all 

 of the form changes, and it is highly probable that some of them, at 

 least, are characteristic of different periods in the life history and that 

 some, at least, are gametes. Further than this, the evidence at the 

 present time does not warrant generalizations. 



The encysted stages of trypanosomes are particularly interesting 

 as an important phase in the life history whereby the organisms are 

 able to withstand unfavorable conditions. The first observations 

 were made by Minchin ('07) in connection with Tryp. grai/i in the 

 posterior region of the gut of Glossina palpalis. The flagellum is 

 retracted and a slime cyst similar to that described by Prowazek in 

 Herpctomonas muacce domesticce secreted. The last trace of the flagel- 

 lum disappears and the nucleus fragments into chromidia, while the 

 kinetonucleus is no longer demonstrable. The cyst wall becomes 

 more definite and resistant, changing the while from an ellipsoidal to 

 a spherical form. Internal changes were not seen beyond evidences 

 of division observed in a few cases. It may be suggested here that 

 chromidia formation and disappearance of nuclei and subsequent 

 division of a nucleus in the cyst may indicate a method of autogamous 

 fertilization similar to that occurring in entameba. 



The "latent bodies" described by Moore and Breinl ('07) are 

 entirely different from encysted forms such as Minchin describes, 

 and different from the encysted forms of Tryp. c/amlnense which they 

 themselves describe as being formed after the action of atoxyl in the 

 blood. These cysts are much larger than the latent bodies and similar 

 to ordinary cysts which free flagellates secrete under abnormal con- 

 ditions. These " latent bodies," which Moore and Breinl regard as the 

 same things seen by Rodet and Vallet, Plimmer and Bradford in 

 infections with Tryp. brucei, and by Lingard in the blood of cattle 



