H PHYLUM PROTOZOA 83 



no trace of contractile vacuole, of flagella or pseudopods, of mouth 

 or gullet. Nutrition is effected entirely by absorption. 



Reproduction takes place by a peculiar and characteristic 

 process of spore-formation. Two individuals come together, 

 and become rounded ofE and enclosed in a common cyst (B), but 

 remain separate. The nucleus of each, after undergoing reduction- 

 changes, divides repeatedly, until a large number of nuclei are 

 formed (0). Each of the nuclei becomes surrounded by a thin 

 layer of protoplasm. The minute cells thus formed, after 

 moving to and fro actively for a time, unite in pairs after the 

 substance of the two individuals has become coalescent (D). From 

 each of the cells or zygotes that are formed by the union of two 

 of the original small cells or gametes, a spore is formed, so that the 

 cyst now comes to contain numerous small spores (E). These are 

 spindle-shaped bodies, each enclosed in a strong chitinoid case (F), 

 and thus differing in a marked manner from the naked spores 

 of the Rhizopoda and Mastigophora. The protoplasm and nucleus 

 of each spore then undergo fission, becoming divided into a number 

 of somewhat sickle-shaped bodies, the falciform young or sporozoiles, 

 which are arranged within the spore-coat somewhat like a bundle 

 of sausages. In all probability the spores pass through the digestive 

 system of a bird, pass out in its faeces, and only undergo further 

 development if taken into the intestine of an earthworm, when the 

 spore-coat becomes dissolved or ruptured and the sporozoites are 

 set free. From the intestine they are able to migrate freely, and 

 pass to the ciliated funnels of the male reproductive system, entering 

 the cells of the ciliated funnels, in which they are said to live for a time 

 as intracellular parasites, and, after a time escape into the cavity of 

 the vesicula and become lodged in the centre of one of the spherical 

 bodies known as sperm-morulce, each made up of a protoplasmic core 

 with an investment of developing sperms (G). Ultimately they 

 become free as trophozoites surrounded for a time by degenerating 

 sperms (H). 



2. CLASSIFICATION AND GENERAL ORGANISATION. 



The Sporozoa are exclusively parasitic, being the only group of 

 Protozoa of which this can be said. They have no organs of 

 locomotion and always multiply by spore-formation. The class is 

 divisible into the following five orders : 



ORDER 1. GREGARINIDA. 

 Sporozoa in which the trophozoite is free and motile. 



ORDER 2. COCCIDIIDEA. 



Sporozoa in which the trophozoite is a minute intracellular 

 parasite. 



o2 



