TRYPANOSOMA 



383 



blepharoplast, because it is an achromatic body connected with a 

 cilium or a fiagellum. 



We now come to a point on which there is a great difference of 

 opinion — viz., the polarity of the parasite. There can be no doubt, 

 in our opinion, that, as a rule, the anterior end of a parasite should be 

 the non-flagellate end, as first suggested by Sambon, because, in 

 wending its way through the blood, that end goes first, and the 

 undulating membrane and fiagellum follow, and blood being the 

 natural habitat of the parasite, this method of propulsion must be 

 considered to be normal. Moreover, morphologists (Woodcock) 

 support this view. There is, however, no doubt that, at times, the 

 flagellate end can be in front. 



Movement is largely caused by the undulating membrane, while 

 the fiagellum assists; but creeping or gregarinoid movements have 

 been noted by Leger, and zigzag movements by Gray and Tulloch, 

 and in both of these the non-flagellate ends go first. In this work 

 anterior, therefore, means the non-flagellate end of the trypanosome 

 and posterior the flagellate end. 



The anterior end is very variable, and may be even amoeboid, 

 while the posterior end is generally tapering, because the cytoplasm 

 extends some way along the fiagellum . 



It has already been noted that the body of the parasite is slightly 

 compressed laterally, and the edge with the undulating membrane 

 is considered to be dorsal. In some species a supporting structure 

 somewhat of the nature of an axostyle has been described. 



The measurements of the parasite are from the non-flagellate 

 extremity to the kinetonucleus, from that to the anterior end of 

 the trophonucleus, from that to the posterior end of the tropho- 

 nucleus, from that to the tip of the fiagellum, the sum of these 

 giWng the length; while the width is taken in the region of the 

 trophonucleus. 



Stephens' method of measurement is, after outHning the parasite, to draw 

 a straight fine on a piece of transparent paper, and to mark one end, which is 

 made to coincide with one extremity of the outUned trypanosome and then 

 transfixed by a vertical needle. The transparent paper is now rotated so that 

 the line runs in the long axis of the parasite. Where it deviates another pin is 

 inserted and the first removed. The transparent paper is again rotated to 

 take in another portion of the axis of the parasite, and this is repeated until 

 all the deviations of the parasite have been followed and the distal extremity 

 reached. 



The results of careful measurements have been to show that some trypano- 

 somes are polymorphic and others are not. 



Food is absorbed by osmosis from the liquid in which the parasite 

 is living. 



Lite-History. — The life-history of a trypanosome is not as yet 

 fully known, but it is recognized that it has an alternation of genera- 

 tions associated with an alteration of hosts, one generation being 

 usually completed in the blood of a vertebrate, and the other in the 

 alimentary canal and its appendages of some blood-sucking in- 

 vertebrate. 



