344 FAMILY: TRYPANOSOMID^ 



growth, multiplication by binary fission may occur. The various forms 

 which occur before the adult flagellate stage is reached have been called 

 jne-fageUates by Patton (19086). When the fully-formed flagellate stage 

 has jjersisted and reproduced for some time, there occurs a gradual retrac- 

 tion of the body towards the leishmania form in preparation for encystment. 

 The forms leading to encystment have been called post-flagellates. These 

 are usually attached to the surface of the cells lining the hind-gut, and are 

 thus haptomonad forms. In the case of the development of trypanosomes 

 in the invertebrate, the final infective forms which pass back to the verte- 

 brate have the trypanosome structure, and have been developed from 

 attached or haptomonad forms of the crithidia type. These infective 

 forms have been termed metacyclic trypanosomes by Brumpt (1913). In 

 the case of some trypanosomes {T. lewisi, T. cruzi, T. melophagium), they 

 are produced in the hind-gut of the invertebrate and escape in the faeces, 

 which are ingested by the vertebrate (development in the posterior station) ; 

 while in others (T. gambiense, T, vivax, T. granulosum) they develop 

 in the anterior part of the alimentary tract, in the salivary glands (tsetse 

 flies), or proboscis sheath (leeches), and enter the vertebrate during the 

 biting act (development in the anterior station). 



CLASSIFICATION. 



The classification of the members of this family is a difficult one on 

 account of the many gaps in knowledge and the contradictory statements 

 made by different observers. The flagellates, which are limited entirely 

 to invertebrate hosts, are handed on from one to the other by encysted 

 forms in the faeces. Those which have both a vertebrate and invertebrate 

 host, as far as is known, always pass from the latter to the former in the 

 unencysted condition. In the case of flagellates of the genus Trypano- 

 soma, the infective forms are of the trypanosome type (metacyclic trypano- 

 somes). The exact form which is infective in the case of members of 

 the genus Leishmania is not known, but it may be assumed that encysted 

 forms are, at any rate, unnecessary. Assuming this to be the case, it is 

 possible to divide the members of the family into two groups — those 

 limited entirely to invertebrates, in which infection is contaminative 

 through one insect ingesting cysts passed by another {Leptomonas, Cri- 

 thidia, Herpetomonas), and those occurring in both vertebrate and in- 

 vertebrate hosts, in which infection is passed from the invertebrate to the 

 vertebrate by the former inoculating unencysted flagellates during the 

 act of feeding or passing unencysted flagellates in its faeces, which either 

 contaminate the puncture wound or are eaten by the vertebrate {Leish- 

 mania, Trypanosoma). The flagellates with two hosts can be divided into 

 two groups according as the highest stage of development is the leptomonas 



