ENTOMOLOGY

DISEASES CARRIED BY FLEAS 353trypanosomes which are contained within an envelope, formed by the periblastof the parent parasite. Inside the periblast envelopes are a numberof daughter trypanosomes wriggling very actively; the envelope finallybursts and releases them, usually about eight, in the host cell. Thedaughter forms escaping from the host cell into the stomach of the fleaare fully formed, long trypanosomes. They then pass into the rectum,where they assume a crithidial phase, and become pear-shaped. Thekinetonucleus has traveled anteriorly past the nucleus toward the flagellum.The crithidial forms attach themselves to the wall of the rectumand multiply by binary fission. In this form the parasite probablyHosr I (RODENT).HosT I MIOr.RATS (EI'IMYS.ACANTHOMYS.Mus.Myoxus. MBRIONZ5).Hosr II fLEAS (CIRATOPHYLLUS.Cn:NOCEPHIILUS.CTBNOPSyLL .... RrLBlC,XBNOPSYLL...).LIFE CYCLE or TRYPANOSOMA LEWISI.,,'Ill, 61. (Pierce,)exists throughout the life of the insect. From the crithidial forms smallinfective trypanosomes develop. These are small, broad, and stumpy,with the kinetonucleus behind the nucleus, and the flagellum longer.B.rumpt (1913) declares that transmission occurs exclusively by rodentslicking up the feces of infected fleas. These feces contain little metacyclictrypanosomes which are able to traverse he~lthy mucous membranes.The life cycle as described has been figured' graphically in 'the samescheme as used in previous lectures.•Trypanozoon nabiasi (Railliet), a rabbit trypanosome, presumablynonpathogenic, attacks the genus Lepus and was found by Brumpt(1913) to be transmitted by the rabbit fleas Ctenocephalus- Zeporis(Leach) Baker and Spilopsyllus lcporis (Leach) Baker. The life cycle