ENTOMOLOGY

DISEASES CAUSED OR CARRIED BY l\HTES AND TICKS 4~1conjugate and the nuclei fuse, and then follows a throwing out of ~wolarge masses of chromatin from the nucleus and the separation of a.port.ion of cytoplasm resulting in the formation of an oocyst with a synkaryon.The oocyst, still imbedded in the epithelial cell, grows rapidly,becoming irregular in form. Later stages of development are onlyfound in ticks which ingest vermicules during their nymphal stage. Theoocyst divides into four cysts which grow very large. These may ruptureand release into the body cavity the sporocysts which contain thesporozoites.After sucking the blood of a dog from two to four days; th!;! adultCYCLE OF SCHIZOGONYIN CA.NI! FAMILIARIS (DOl)OvCLE 0 F SPOROGONYIN RHIPICEPHAL.US SANGUI"£US(no. TICK).LIfE CYCLE OF HAEMOGREGAlM CANIS.THECAUSE OF CANtNI;: ANEMIA.(CO ... TlluanuArru D~HRlPTIO'""'ND o.."WIIII •• BY CHRlsroPHCRs)FlO. 79.-(Pierce).tick drops off never to feed again. It IS apparent then, that the adulttick taking up infected blood for the first time in this stage of its development,cannot of itself transmit the disease, as the parfisite has been shownby Christophers not to complete its development in the adult. We must,therefor~, look to the life history of the tick to find the possible methodof transmission. Christophers found that complete development in thetick only occurs when the parasite is taken up in the nymphal stage. Hedid not find any parasite in larvre fed on infected dogs. After the nymphalstage the ticks drop oft' from the host for molting. They then reattachas adults and engorge. The possibility of infecting a new' host is verygreat because of this change. of host during the development of theparasite in the tick.