316 



FAMILY: TRYPAXOSOMIDiE 



forms noted by Roubaud and Swingle. At any time, probably with the 

 advent of fresh nutriment into the intestine, these attached forms may 

 become free, and, as a result of increase in length of the axoneme, develop 

 flagella for a swimming mode of life. 



ORIENTATION AND ORIGIN OF THE DIFFERENT TYPES. 



It will be seen that in the simplest flagellate type, the leptomonas, the 

 flagellar end is undoubtedly anterior, for the living organism progresses 



in this direction, and in the more 

 highly constructed trypanosomes 

 with undulating membranes the 

 flagellar end, according to the 

 view expressed above, is still 

 anterior. In the blood of certain 

 fish there occurs another type 

 of flagellate, the trypanoplasm, 

 which possesses two flagella 

 (Fig. 151). During progression, 

 one is directed forwards and the 

 other, attached to an undulating 

 membrane, backwards. There is 

 little doubt that the anterior end 

 of this organism is the one from 

 which the f orwardly directed free 

 flagellum arises, and it has been 

 supposed by some that the try- 

 panosome type has been derived 

 from these forms by the suppres- 

 sion of the free flagellum. It 

 will be evident that, if this is the 

 case, the flagellar end of a try- 

 panosome must be regarded as 

 posterior. The evidence in favour 

 of trypanosomes as they occur 

 in vertebrates having originated 

 from the leptomonas and crithidia forms of invertebrates seems almost con- 

 clusive, while the trypanoplasms undoubtedly belong to quite another group 

 of flagellates (see p. 637). Leger, L. (190%), expressed the opinion that 

 some trypanosomes had been derived from a trypanoplasm ancestor 

 (trypanosomes with flagellum posterior), while others had originated from 

 leptomonas ancestors (trypanosomes with flagellum anterior). Liihe (1906) 



Fig.. 151. — Trypanoplasms from Fish 

 (x 2,000). (After MiNCiiiN, 1909.) 



1. Trj/panoplasma keysselitzi of the tench. 



2. Trypanoplasma ahramidis of the bream. 



3. Trypanoplasma borreli of the rudd. 



