XXIII] MORPHOLOGY 385 



in the development of these large trypanosomes vary consider- 

 ably in their dimensions. The smaller parasites measure about 

 18 microns in length by 2 microns in breadth, and all stages 

 in their increase in size may be observed. In the small forms 

 the kinetonucleus is frequently situated alongside the tropho- 



B 



Fig. 88. Trypanosoma theileri. x about 1500. A. Small crithidial form; 

 B. Large individual from the blood of a cow. (After Theiler.) 



nucleus in the middle of the body of the trypanosome, and the 

 undulating membrane is only slightly developed. In the 

 larger parasites of the theileri type, the kinetonucleus is situated 

 towards the posterior extremity and the trophonucleus about 

 the middle of the body. The undulating membrane is very 

 large and thrown into bold folds ; anteriorly the flagellum is 

 free for a distance equal to about one-quarter the length of the 

 body of the parasite. The protoplasm contains large numbers 

 of granules and stains very deeply. 



The only mode of multiplication that has been observed is 

 simple longitudinal division, which is of the normal type. 



Mode of transmission. Theiler has shewn that this trypano- 

 some may be carried from one animal to another by means 

 of Hippobosca. " For this purpose some flies were kept over- 

 night in order to make them hungry, and were then placed on 

 the groins of an infected calf. To give the experiment every 

 chance of success, the spot where the flies were put to feed was 

 first shaved, as was also the spot on a clean animal where they 

 were placed for infection. Feeding by turns on a sick and on a 

 clean animal was thus repeated several times, in order to secure 



H. B. F. 25 



