382 



TR YPA NOSOMIDM 



which ends in a little bead — the blepharoplast — from which the 

 flagellum, which is also composed of chromatin, arises, A more 

 primitive arrangement is for the kinetonucleus to contain the blepha- 

 roplast, which is really only a centrosome. Under these circum- 

 stances the flagellum will arise from the kinetonucleus. When the 

 blepharoplast is separate from the kinetonucleus it is a moot point 

 as to whether there is or there is not another centrosome in that 

 nucleus. 



The flagellum runs outwards through the endoplasm to the ecto- 

 plasm, which it raises into a membrane, the undulating membrane, 

 and turns, and runs along the remaining length of the cytoplasm, in 

 which it may end, or it may project as a free lash beyond the cyto- 

 plasm. In this course it presents three portions: (i) The root in 

 the endoplasm; (2) the undulating portion in the ectoplasm, and 

 (3) the free portion. In some stages of the life-history the flagellum, 

 instead of turning along the undulating membrane, projects from 

 its blepharoplast through the endo- and ecto-plasm to thejoutside 

 of the parasite. 



anterior end ^ undulating membrane ^ flagel lum 



kinetonucleus trophonucleus chromatoid granules 



Fig. 88. — Diagram showing the Structure and Polarity of a 

 Trypanosome. 



The undulating membrane, therefore, is the layer of ectoplasm 

 (periplast) raised from the surface of the parasite by the second 

 portion of the flagellum along a line sometimes called dorsal, and 

 may be prolonged a certain distance along what is generally con- 

 sidered to be its free portion. The membrane is variously described 

 as being homogeneous or strengthened by myonemes as in Hcemo- 

 proteus noctucB. 



Besides these structures the endoplasm often contains a vacuole, 

 looked upon by some observers as a contractile vacuole, while others 

 deny its existence. There is no doubt about its existence in Try- 

 panosoma castellanii. Chromatoid granules can also be seen in 

 the cytoplasm. 



Before leaving this part of the subject it must be noted that 

 many authors have given various names to the trophonucleus, 

 kinetonucleus, centrosome, and blepharoplast. We use the terms 

 in the same sense in which they have been used by Minchin and 

 Woodcock — viz., the principal nucleus is a trophonucleus, because 

 it is believed to be largely concerned in nutrition; it contains an 

 achromatic body, which is the centrosome. The smaller nucleus 

 is a kinetonucleus, because it is mainly concerned in motion; while 

 the little bead connected with the flagellum is looked upon as a 



