THE H^MOFLAGELLATES. 279 



petomonadine forms, of whicli mention has above been made. 

 Moreover, in this parasite the primary host is also the defini- 

 tive one, or that in which the sexual process takes place. 



Turning next to the Heteromastigine forms we are led to 

 the same conclusion, though on more general grounds, for we 

 lack, at present, an illustrative series like that just referred 

 to. For instance, with regard to the origin of the undulating 

 membrane. In Trypanoplasma, which is most probably 

 to be derived from a Bo do -like ancestor, the undulating 

 membrane very likely arose, as Doflein (19) points out, as 

 the result of the contiguity of the trailing flagellum to the 

 side of the body, which led to fusion without loss of motility 

 and thus brought about the development of a membranous 

 expansion. Now there are one or two forms which possess 

 an undulating membrane, but which are not, however (so 

 far as is known), Haematozoan parasites, namely, Try- 

 panophis grobbeni, which inhabits the coelenteric cavity 

 of Siphonophores, and an enteric form parasite in Box 

 bo ops, which Leger (70) regards as a Try pano plasma 

 (intestinalis), but which appeal's to the writer, if anything, 

 nearer Trypanophis (see below, in Systematic). Hence it 

 would seem that the presence of an undulating- membrane in 

 a Trypanoplasmatine form does not necessarily imply a hgemal 

 habitat. 



In connection with this derivation of the Heteromastigine 

 forms it is interesting to note the gradual change in the 

 degree of development of the flagella which can be traced. 

 Starting with Bodo lacertee, both flagella are of equal 

 length, and the trailing one does not reach the posterior 

 limit of the body. In Trypanophis grobbeni (fig. 41) the 

 posterior flagellum is more developed than the antei'ior one, 

 and, of course, attached to the side of the body. Its free ter- 

 mination, however, is very short. In T. (Trypanoplasma) 

 intestinalis this is longer and more strongly developed 

 (fig. 40), though still shorter than the anterior flagelkim itself. 

 In Trypanoplasma borreli (tig. 17 p, g) the anterior 

 flagellum and the free portion of the hinder one are of equal 



