12 NATURAL HISTORY OF SLEEPING SICKNESS 



Let us now look a little more closely at the MastigopTiora. 

 The group is divisible into six sub-groups, ^ but only that 

 which includes the Trypanosomes need be mentioned 

 here. This is named Protomonadina, and includes the 

 following genera : 



1. Trypanosoma. — There is a single flagellum arising 



near the posterior nucleus and continued forwards 

 as a marginal flagellum of an undulating mem- 

 brane ; usually continued into a free flagellum. 

 The species are found mostly in blood and in the 

 digestive tracts of invertebrates, but are also forms 

 in the life cycle of species wholly parasitic in 

 insects. 



2. Trypanoplasma. — There are two flagella, the posterior 



one united to the body by an undulating membrane 

 along most of its length. According to their 

 mode of life they fall into three groups. 



1. Parasites in the blood of fresh- water fish 

 and in the digestive tract of leeches. 



2. Parasitic in the digestive tract of marine 

 fishes. 



3. Parasitic in invertebrates. 



3. Crithidia. — A single flagellum arises about the middle 



of the body and runs forwards to form the marginal 

 flagellum of a short or rudimentary undulating 

 membrane, and is continued beyond as a free 

 flagellum. 



Crithidia occur as parasites in the gut of insects 

 or as a stage in the life cycle of a Try- 

 panosome. 



4. Lepfomonas or Herpetomonas. — There is a single 



anterior flagellum but no undulating membrane. 

 These are parasitic on invertebrates, chiefly 

 insects, but also occur as a form of the next genus 



^ This classification is taken from Minchin. 



