STRUCTURE AND CLASSIFICATION OF PROTOZOA 11 



tion or division of the organism the presence of a 

 nucleus seems essential (fig. 8, n). 



Food Particles. — Minute aggregates of solid par- 

 ticles, sometimes showing their organic and adven- 

 titious nature when they are incapable of being 

 completely digested (fig. 8, r). 



Globular Bodies and Contractile Vesicles. — The 

 former are spherical spaces filled with an oily-looking 

 liquid, often surrounded by an empty space (vacuole) ; 

 they probably represent stages in the digestive process 

 on organisms taken in as food. The liquid inclusion 

 has been proved, in the case of certain protozoa, to be 

 of an acid nature. 



The latter are capable of undergoing contraction 

 during the life of the organism (fig. 8, v). 



Crystalline Bodies. — In certain of the protozoa, 

 as amoeba, granules of a crystalline form occur, 

 which are refractive ; they are thought to represent 

 the final stage in the digestion of the food taken in 

 by the organism before it is assimilated by the 

 protoplasm (fig. 8, c). 



The protozoa increase by fission or binary di- 

 vision and by the formation of zoospores. The 

 first stage in the process of subdivision is the 

 division of the nucleus. This takes place either by 

 the simple process of binary division (fig. 9) or by 

 the more complex- and beautiful process of karyo- 

 kinesis (fig. 10), in which the nuclear body is in- 

 vested with strands of chromatin threads, becoming 

 elongate and constricted in hour-glass form, and finally 

 separated into two distinct bodies, the surrounding 



