262 



ENTOMOLOGY 



m 



tine in form and with no definite cell- wall. A round or oval nucleus is 

 present, also a peculiar chromatin body situated often near the poste- 

 rior end of the cell and termed the blepharoplast. Along one side of the 

 cell is a delicate protoplasmic contractile membrane, the undulating 

 membrane, along the edge of which is a marginal cord, which arises by 

 growth from the blepharoplast and is continued beyond the anterior 

 end of the cell as a vibratile flagellum. 



Asexual reproduction is by means of a longitudinal division of the 

 cell body, preceded by division of the flagellum, blepharoplast and 

 nucleus, the nucleus dividing amitotically. In 

 regard to the existence of sexual stages, or 

 gametes, the results of investigators seem to 

 be inconclusive as yet. 



In a film of fresh blood under the microscope, 

 any active trypanosomes in the field of view 

 attract attention as centers of commotion among 

 the red blood corpuscles, which are pushed aside 

 by the lashing, twisting and other movements of 

 the trypanosomes. 



The nutrition is by means of osmosis. Try- 

 panosomes have not been seen to attack erythro- 

 cytes, but according to MacNeal and Novy 

 haemoglobin is useful if not indispensable to 

 them. 



All five classes of vertebrates serve as hosts 

 for trypanosomes, of which more than seventy 

 species have received names. Most of these 

 species are carried from one vertebrate host to 

 another by means as yet unknown, but about 

 20 per cent, are known or suspected to be 

 transmitted by an intermediate invertebrate host. Thus trypano- 

 somes of frogs are conveyed by leeches; pigeons are infected by mos- 

 quitoes, rats by sucking lice and fleas, and many mammals through the 

 agency of blood-sucking flies of the genus Glossina, and probably also 

 by Stomoxys and certain Tabanidse. 



Tsetse Flies. The name tsetse fly, originally limited to Glossina 

 morsitans (Muscidae) is now used for any of the fifteen known species 

 of the genus. These flies are a little larger than the common house fly 

 (Musca domesticd) . Their wings, in the resting position, overlap exactly 

 (Fig. 275) instead of being separated at the tips. The proboscis pro- 



u 



FIG. 274. Trypano- 

 soma lewisi. b, blepharo- 

 plast; /, flagellum; m, 

 marginal cord; n, nucleus; 

 u, undulating membrane. 

 .Greatly magnified. 



