THE PROTOZOAN SUBGROUPS 329 



of this membrane throughout its length, and may terminate with the 

 membrane or be continued beyond the body as a free lash." 



All species of the genus Trypanosoma show a general morphologic 

 similarity. In general they may be said to measure from 15-45 microns 

 in length, including the flagellum, and 1-5 microns in thickness. As 

 typical of the group, T. theileri, living exclusively in the blood of cattle, 

 may be taken for brief description. The body is spindle-shaped, more 

 or less serpentine, and pointed at the ends, from one of which there pro- 

 jects a vibratile flagellum. The flagellum is continued as a marginal 

 cord toward the opposite end of the body where it takes origin in a 

 minute granule (blepharoplast). In close relation to this granule is a 

 deeply staining body which, because of its connection with the motile 

 elements of the cell, has been designated the kinetonucleus. Arising 

 from the kinetonucleus, the flagellum passes along the body on the 

 border of a dehcate protoplasmic membrane — the undulating mem- 

 brane — toward its free extremity. Centrally located is the tropho- 

 nucleus, the nucleus concerned with the vegetative processes of the cell. 

 This is clearly defined and usually has the chromatin in the form of 

 granules of definite nimiber. The endoplasm is granular and may 

 appear vacuolated. Reproduction in the blood of the vertebrate host 

 is by longitudinal division following division of the blepharoplast, 

 kinetonucleus, and trophonucleus. In some cases the daughter cells 

 remain together for a longer or shorter time in a sort of rosette forma- 

 tion. 



The members of the genus Trypanoplasma (Cryptobia) have two 

 flagella. They are mostly parasitic in fishes; so far as known there are 

 no species which attack higher animals. 



Transmission. — The Trypanosoma are parasites of the blood, 

 IjTnph, or cerebrospinal fluid of vertebrates, and, with one known ex- 

 ception, their transfer is accompKshed by the intervention of an inter- 

 mediate carrier which is either essential and indirect, or mechanical 

 and direct. In the former case a blood-sucking fly becomes infected 

 by feeding upon the blood of an animal harboring the trypanosomes. 

 In the body of the fly the trypanosomes undergo certain changes, 

 probably of a revitalizing nature, and for a period of time the fly remains 

 noninfective. When this period has elapsed the trypanosomes within 

 the fly resume their ability to infect any host whose blood is reached by 

 the piercing mouth parts of the fly. Furthermore, such flies remain 

 infective for an indefinite period, probably for the remainder of their 

 lives. 



By the direct or mechanical method of transfer the fly, after having 

 bitten an infected animal, very shortly afterward visits a healthy one 

 and may inoculate it directly with its contaminated proboscis. If the 

 fly draws the blood of a sick animal and then successively visits two 



