58 THE ANIMAL PARASITES OF MAN 



development ; it may be pointed or obtuse. The opposite end is 

 the posterior extremity ; it always tapers to a point and is con- 

 tinued by the free end of the flagellum. Most authors call the 

 posterior extremity anterior, because, as a rule, trypanosomes move 

 more rapidly and, apparently, more frequently with this end 

 foremost ; but the direction of locomotion is not a good argument , 

 otherwise we should have to call the posterior extremity the well- 

 developed head of Cephalopods, simply because these animals move 

 more rapidly with the tail end foremost, and thus escape the 

 animals that prey upon them. A comparative examination of 

 the flagellates, and especially of the free-living forms, shows very 

 clearly that the true anterior extremity is that from which the 

 flagellum arises. In most genera the flagellum is not only an. 

 organ of locomotion, but also an important means for the capture 

 of food. In such forms as Euglena the anterior extremity is 

 provided with an oral cavity which opens at the base of the 

 flagellum. In Euglena the flagellum is entirely free and sways 

 in front of the head of the creature, like a proboscis, and, indeed, 

 it was called proboscis by Ehrenberg. In trypanosoma, the 

 flagellum bends directly backwards and is attached, for a con- 

 siderable portion of its length, to the body by a thin web of 

 body plasma. The flagellum is composed of chromatin. In cer- 

 tain stages it is cast off. It is easily reproduced by the blepharo- 

 plast. When cast it may continue to move independently for 

 some time. Adjoining or surrounding the blepharoplast is a clear 

 area called the vacuole ; it probably represents the contractile 

 vesicle of other flagellata. Sometimes the plasma of stained speci- 

 mens is beset with a variable number of dark-staining granules ; 

 these granules represent reserve material and are called chromato- 

 phores. 



By examining large numbers of trypanosomes during the course 

 of a trypanosoma infection, one soon notices that the parasites 

 vary considerably in size and shape. A more careful study 

 enables us to group these various forms into three distinct types ,. 

 corresponding to the well-known forms of the H ' cemamcebidce found 

 in the blood of malaria patients. 



The most frequent form is the asexual form, which multiplies 

 very rapidly by simple longitudinal division. It is usually seen 

 in the process of division. This process begins most frequently 

 with the division of the blepharoplast, which elongates and then 

 divides. The nucleus divides almost simultaneously, sometimes 

 before the blepharoplast. The division of the blepharoplast brings 



