of Trypanosoma lewisi in the Rat Flea. 533 



the fleas taken haphazard from infected rats, we think it possible 

 that these forms represent the final stages of development. If so, 

 we are unable to say in which way these small trypanosomes 

 return to the rats' blood. We have not been able to find any 

 flagellated form either in the coelom or salivary glands of infected 

 fleas. 



At present the broad fact remains established by a proper 

 system of controls that T. lewisi undergoes a morphological cycle 

 of development in the gut of its invertebrate host. 



35—2 



