DISEASES CARRIED BY FLEAS 



353 



trypanosomes which are contained within an envelope, formed by the peri- 

 blast of the parent parasite. Inside the periblast envelopes are a number 

 of daughter trypanosomes wriggling very actively ; the envelope finally 

 bursts and releases them, usually about eight, in the host cell. The 

 daughter forms escaping from the host cell into the stomach of the flea 

 are fully formed, long trypanosomes. They then pass into the rectum, 

 where they assume a crithidial phase, and become pear-shaped. The 

 kinetonucleus has traveled anteriorly past the nucleus toward the flagel- 

 lum. The crithidial forms attach themselves to the wall of the rectum 

 and multiply by binary fission. In this forai the parasite probably 



SPOROGONY 



Host I Mice,Rats (Epimys.Acanthomys, ^fus,lVlYoxus, Meriones). 



HoSrU Fleas fCERATOPHYLLUS.CTENOCEPHALUS.CTENOPSYLLA.PuLEX, 



Xenopsylla). 



LIFE CYCLE OF TRYPANOSOMA LEWISI. 



I"' 111. a J. (Pierce.) 



exists throughout the life of the insect. From the crithidial forms small 

 infective trypanosomes develop. These are small, broad, and stumpy, 

 with the kinetonucleus behind the nucleus, and the flagellum longer. 

 Brumpt (1913) declares that transmission occurs exclusively by rodents 

 licking up the feces of infected fleas. These feces contain little meta- 

 cyclic trypanosomes which are able to traverse healthy mucous mem- 

 branes. 



The life cycle as described has been figured graphically in the same 

 scheme as used in previous lectures. 



Trypanozoon nahiasi (Railliet), a rabbit trypanosome, presumably 

 nonpathogenic, attacks the genus Lepus and was found by Brumpt 

 (1913) to be transmitted by the rabbit fleas Ctenocephalus leporis 

 (licach) Baker and Spilopsyllus leporis (Leach) Baker. The life cycle 



