708 H. JI. WOODCOCK. 



as being phases in the life-cycle of some vertebrate trypaiio- 

 some, we find at once a fundamental resemblance, while in 

 one or two particular cases there is a sti-ikingly close 

 similarity in detail. It would occupy too much space to 

 follow out tins comparison at length. I must content myself 

 with a reference to various papers, and with a few indications 

 as to the chief points of agreement. 



It may be noted, as a preliminary, that I follow Patton's 

 definition of, and distinction between, a herpetoraonad form 

 and a crithidial or trypanomonad form ; the terms "critliidial" 

 and " trypanomonad " are practically interchangeable, but I 

 prefer to use the latter, at all events when referring to this 

 phase in connection with a vertebrate trj'panosome.^ Fur- 

 ther, it is necessary to emphasise the fact that the characteri- 

 sation of these two types is based upon their structure when in 

 the active, extended, flagellate condition ; in other words, the 

 diagnostic form of the parasites is only seen when they are in 

 this condition. Rounded, resting phases, whether possessing 

 a flagellum or lacking one, cannot be regarded by themselves 

 as representing either a herpetomonad or trypanomonad 

 phase, simply because, when the parasites ai-e in this con- 

 dition, the features used for distinguishing between the two 

 types are not present. It is certainly due to Patton that we 

 are at last able to realise that there are these two perfectly 

 definite types, a herpetomonad and a crithidial or tr^^pano- 

 nionad one, and to distinguish clearly between them. Until 

 Patton separated the two types upon the above basis, the 

 greatest confusion often prevailed as to whether a given 

 parasite belonged to one or the other; and it must be 

 admitted this confusion was chiefly due to the unsuitable 

 diagnostic characters used by Leger in his earliest descriptions 

 of these forms. 



The memoirs in question are those by Miss Robertson (23, 

 24, and 25), Minchin (11), Prowazek (22), Stuhlmann (31), 

 and Roubaud (26). In all the parasites described, namely, T. 



^ There have been, hithei-to, two quite different meanings attached to 

 the term " crithidial " (cf . also below). 



