280 H. M. WOODCOCK. 



length. In T. cyprini (fig. 17 h) the former is mucli shorter 

 than the latter, and shows signs of reduction, while in Try- 

 panosoma it is entirely lost. 



Hence, while it is very probable that the condition of the 

 locomotor apparatus in Trypanophis represents a phylo- 

 genetic stage in the development of the condition found in 

 Trypanoplasma, this form itself is not of much assistance in 

 determining the original kind of host of the Heteromastigine 

 Haemoflagellates. 



The reasons for thinking that this section of the H^mo- 

 flagellates is also derived from a primitively Invertebrate 

 type are, as a matter of fact, the considerations fully dis- 

 cussed in Section IX, which point, on the one hand, to the 

 possession by the parasites of an alternate, Invertebrate host, 

 in which conjugation takes place, and, on the other hand, to 

 a relationship between the Trypanosomes and the Hgemo- 

 sporidia. For, on a priori grounds, we may reasonably 

 infer that the definitive host is the primary, original one. 

 Thus would be explained the necessity which exists in most, 

 if not all, H^ematozoa for the return of the parasites to the 

 alternate host. Again, both sections of IlEemosporidia, those 

 of warm- and of cold-blooded Vertebrates, have recently been 

 brought into line in respect of the occurrence of conjugation 

 only in the Invertebrate (see Introduction, p. 161) . It follows, 

 therefore, that all evidence pointing to a connection between 

 the two " groups " of Haematozoa at the same time favours 

 the view here put forward. 



While, of course, the possibility of a Hasmatozoan being 

 derived from a form primarily parasitic in the intestine of a 

 Vertebrate must not be ignored, the writer agrees, never- 

 theless, with Leger, who aptly remarks that one is not 

 justified in so deriving any H^emoflagellate until a coclomic 

 form, known with certainty to undergo sexual conjugation in 

 the Vertebrate, has been found. ^ 



' Even in the case of T. equiperdum, the fact that the parasites are 

 transmitted directly from one Vertebrate to another, during the act of 

 coitus, does not imply that this form has never possessed a definitive Insectan 



