DISEASES CAUSED OR CARRIED BY MITES AND TICKS 421 



conjugate and the nuclei fuse, and then follows a throwing out of two 

 large masses of chromatin from the nucleus and the separation of a 

 portion of cytoplasm resulting in the formation of an oocyst with a syn- 

 karyon. The oocyst, still imbedded in the epithelial cell, grows rapidly, 

 becoming irregular in form. Later stages of development are only 

 found in ticks which ingest vermicules during their nymphal stage. The 

 oocyst divides into four cysts which grow very large. These may rupture 

 and release into the body cavity the sporocysts which contain the 

 sporozoites. 



After sucking tlie blood of a dog from two to four days, the adult 



Host I (Dog). 



TiCK ON Host I(NymphorAoultI 



CvcLE OF Schizogony Cycle of Sporogony 



lNCA^alS FAMILIABIS (Dos) JN R HI PICEPH ALUS SANGUINEUS 



(Dog Tick). 



LIFECrCIIOFHAEMOGREGARINACANIS. 



TheCausezof Canine Anemia. 



(CoNSTRucnDArriRDtsoHiPTiONS AND Dbawinos bv ChristopmersJ 



Fig. 79.— rPierce). 



tick drops off never to feed again. It is apparent then, that the adult 

 tick taking up infected blood for the first time in this stage of its develop- 

 ment, cannot of itself transmit the disease, as the parasite has been shown 

 by Christophers not to complete its development in the adult. We must, 

 therefore, look to the life history of the tick to find the possible method 

 of transmission. Christophers found that complete development in the 

 tick only occurs when the parasite is taken up in the nymphal stage. He 

 did not find any parasite in larva* fed on infected dogs. After the nymphal 

 stage the ticks drop off from the host for molting. They then reattach 

 as adults and engorge. Tlic possibility of infecting a new host is very 

 great because of this ' change of host during the development of the 

 parasite in the tick. 



