Morphology and classification 



165 



cycle takes place in a tick, and is in part analogous to that de- 

 scribed for Plasmodium. The stages are not fully known, but the 

 infectivity of the tick is transmitted to the offspring in the case of 

 the Texas-fever tick {Rhipicephalus {Boophilus) annulaius). 



Nosema. — The sporozoa above described all belong to the 

 Telosporidia, organisms which end their individual existence at 



Fig. 83.— Diagram of the developmental cycle of Nosema bombycis. C, Cell of 

 the intestinal epithelium containing asexual multiplication forms and showing their 

 transition into spores, a, b, c. Spores, the last with polar thread, d. Ameboid form 

 emerging from the spore to penetrate a new host cell at k. (From Doflein after 

 Stempell.) 



the stage of spore formation. A second large subdivision of the 

 sporozoa is named Neosporidia. In this group the spores are 

 formed without terminating the existence of the individual. The 

 parasites of this type are comparatively small and not very well 

 known. They are often spoken of as microsporidia or psorosperms . 

 The best-known form is Nosema bombycis, the cause of Pebrine in 

 silkworms. 



