270 H. M. WOODCOCK. 



Trypauomorpha (Trypanosoma) noctuee and Hcrpeto- 

 monas. In all known respects there is either entire agreement 

 between the two genera, or the condition found in the former 

 is easily derivable from that existing in the latter. Certain 

 species of Herpetomonas may well represent a phylogene- 

 tic stage in the evolutionof Trypanomorpha; indeed, in some 

 cases — especially Avliere they have been described from blood- 

 sucking Insects — parasites identified as Herpetomonads pro- 

 bably themselves constitute, in reality, only a phase in the 

 life-cycle of a particular Hasmoflagellate. As Leger points 

 out, Crithidia fasciculata itself is very likely a Haemo- 

 flagellate, and closely allied to Trypanomorpha, though 

 exactly how closely cannot be said until its life-history in the 

 Vertebrate host has been investigated. 



Many, perhaps most, authorities regard all uniflagellate 

 Trypanosomes as descended in this manner, and as agreeing 

 with Trypanomorpha in having the flagellum at the 

 anterior pole of the body. There are, however, in the writer's 

 opinion, several cogent reasons against accepting this view, 

 reasons whicb, on the contrary, lend considerable support to 

 the alternative theory that, at any rate, most Trypanosomes 

 (sensu stricto) are derived from a type like Trypano- 

 p las ma by the loss of the anterior free flagellum, so that the 

 non-flagellate end is i-eally the anterior one.^ These reasons 

 are best discussed under two headings, dealing, respectively 

 (a) with biological or physiological considerations, and {h) 

 with certain morphological points. To the former particular 

 weight must be assigned, and the indications which they 

 aiford are borne out and, in fact, strengthened by a considera- 

 tion of the latter. 



(a) It may, we thiuk, be fairly assumed that the sensory 

 extremity of a HtDmoflagellate is, as in non-parasitic Flagel- 

 lates, the anterior end. By the sensory extremity is here 

 meant that region of the body which is most in touch with 

 the environment ; the region specially concerned with the 

 adjustment of the voluntary relations of the parasite to the 

 Tliis view was lirst outlined by Leger (65). 



