ANIMALCULES AS PARASITES 207 
are dissolved by the digestive fluids, and the soft protoplasmic 
contents make their way into the cells which line the intestine, 
there to develop into worm-like gregarines. 
A great number of the Sporozoa are excessively minute 
parasites living within the bodies of hosts of various kinds, and 
often giving rise to disease. It has been proved, for example, 
that malarial fever is due to a blood parasite of the kind intro- 
duced by the agency of a Mosquito (Axopheles). The complex 
life-history of this form will be briefly given in the section on 
ANIMAL FOES. 
