16 THE PROTOZOA. 



mass or zygote, and within this spore-coat the zygote 

 divides four times, producing eight sporozoites. As 

 all these events take place in the cyst formed about 

 the two gametocytes, a very large number of spores 

 are enclosed in such a sphere. Hence the term 

 ' Monocystis.' 

 Examine prepared sections of a vesicula containing many 

 Monocystis. 



The' fate of these spores, each containing eight 

 sporozoites, is uncertain. They are probably eaten 

 together with the worm, by thrushes and other birds, 

 scattered over the ground with the droppings and 

 washed into the soil, whence they are again taken 

 up by earthworms. In the worm the spore-coat is 

 probably digested, releasing the sporozoites, which 

 then migrate into the vesicula? and become tro- 

 phozoites. 



VI. TRYPANOSOMA. 



Trypanosomes (' Boring-bodies ') are Protozoa living in 

 the blood or other tissues of animals and of man. The animal 

 so infected is said to be the host ' and the Trypanosome the 

 ' parasite.' Disease of the host does not necessarily accom- 

 pany the presence of Trypanosomes, since many affected 

 animals have in course of time acquired immunity. 



There are many kinds of Trypanosomes, but one of the 

 largest is found in the blood of the dogfish, and another 

 closely similar form occurs in the skate. The following 

 description applies to either. 



Clean a centrifuge-tube and place in it a few cubic centi- 

 metres of the blood of a freshly killed dogfish or skate. Insert 

 the tube into the centrifuge-machine and rotate it for a few 

 minutes, taking precautions to ensure the safe working of the 

 apparatus. When the motion has stopped remove the tube. All 

 the blood corpuscles will now be at the bottom. 



With a fine clean pipette suck up a little of the sediment and 

 place it in a drop of the plasma on a slide. Cover and examine 

 with low and high power of the microscope. Place another drop on 



