152 H. M. AVOODCOCK. 



Class. — Mastigophora. 



Sub- class. — Flagellata. 

 Order. — Lissoflagellata. 

 Sab-order. — Monad in a. 



Fanl^l3^ — Trypanomorpliida), n. fam. 

 Grenus. — Trypano morplia/ n.g. 

 S ub-order. — H eteromastigina. 



Family. — Trypanosomatida?, Dofl. emend. 

 Genera. — Trypanopliis," Trypauoplas ma, 

 Trypanosoma. 



Section I. Characteristics. 



The Ha3moflagellates, altliongli possessing in common a 

 uniform type ot* organisation, are probably not to be con- 

 sidered as all belonging to a single, well-defined group of 

 monophyletic origin. They constitute, rather, an assem- 

 blage of forms springing from at least two different stocks, 

 the resemblances which they exhibit being due to con- 

 vergence, brought about by the acquirement of similar adap- 

 tations in response to their similar and highly-specialised 

 mode of life. They are entirely parasitic, their characteristic 

 habitat being the blood of a Vertebrate. It is unlikely, 

 however, that, in the majority of cases, the whole life-cycle 

 is undergone in that host. The transmission of the parasites 

 from one Vertebrate individual to another is by means of a 

 blood-sucking Invertebrate, Avhich, in several instances, is 

 now known to be a true alternate host, and not merely a 

 carrier ; indeed, it is becoming more and more probable that 

 an alternation of hosts normally occurs in each life-history. 



' Tlie name for this geiuis has heen kiiully suggested by Pruf. Leger. 

 The writer desires, here at the outset, to warmly thank Prof. Leger for 

 much advice and assistance, especially in connection with the section on the 

 derivation and phylogeny of the Trypanosomes. 



^ Altliougli Trypan oph is is most probably not a liajnial parasite, it is 

 included in this article since it is undoubtedly closely' related to Trypano- 

 p las ma. 



