io SOME MINUTE ANIMAL PARASITES 



mammals, birds, and reptiles. Casual or contamina- 

 tive methods of infection are responsible for many 

 maladies, and fouled food-supply is usually to be 

 suspected. A bee disease, due to a parasite, Nosema 

 apis, is spread by bees eating honey contaminated by 

 already diseased bees. Coccidiosis in poultry and 

 game remains for years in a district once heavily 

 infected. The grit and soil are laden with spores 

 from the faeces of infected birds, and the resistant 

 forms of the parasite have been shown to remain 

 infective for a prolonged period after they have left 

 their first host. Wind and rain are also known as 

 active distributing agents of some diseases. 



The gradual development of the parasitic habit 

 sheds an interesting light on the evolution of certain 

 groups. The free-living and thus more independent 

 of the Protozoa spend their lives in either fresh or 

 salt water. Among these are the spirochaetes. 

 Forced by circumstances or guided by choice, other 

 spirochaetes have migrated into the jelly-like organ 

 known as the crystalline style in the food canal of 

 certain molluscs, such as oysters. They can move 

 about in this medium as freely as in water, but they 

 represent an advance in the evolutionary order. 

 Water spirochaetes are ingested by other higher 

 animals with their drink. Some of the spirochaetes 

 so taken adapt themselves to life in the intestine of 

 their hosts, and thus are found in the alimentary 

 canal of such birds as the grouse. Lastly, spiro- 

 chaetes can be ingested and pass into the blood- 

 stream of their host, or they may be inoculated into 

 the host's blood from the alimentary canal of some 



