PHYSIOLOGICAL ACTIVITIES OF THE PROTOZOA 



99 



differences to take into account, the use of the term spore has been 

 very ambiguous and misleading, and protozoologists have given it up 

 for two other terms, sporozoite and merozoite, now generally adopted. 

 The term sporozoite is used to designate those spores or germs that are 



Fig. 36 



Life cycle of Coccidium schubergi. (After Schaudinn.) .Sporozoites penetrate epithelial 

 cells, and grow into adult intracellular parasites (a). When mature, the nucleus divides re- 

 peatedly (6), and each of its subdivisions becomes the nucleus of a merozoite (c). These enter 

 new epithelial cells, and the cycle is repeated many times. After five or six days of incuba- 

 tion, the nierozoites develop into sexually differentiated gametes; some are large and well 

 stored with yolk material {d, e, f); others ha^-e nuclei which fragment into many smaller par- 

 ticles ("Chromidien"), each granule becoming the nucleus of a microgamete or male cell {d), 

 h, i, j) . The macrogamete is fertilized by one microgamete ((/), and the copula immediately 

 secretes a fertilization membrane which hardens into a cyst. The cleavage nucleus divides 

 twice, and each of the four daughter nuclei forms a sporoblast (A-) in which two sporozoites are 

 produced U). 



produced after fertilization, while merozoite is used for the asexually 

 produced germs. The protected sporozoites have the power to carry 

 the disease from one host to another, while the merozoites, as a rule, 

 carry the infection only from one part of the host to another part 

 (Fig. .36). Sporozoites, therefore, have the full potential of vitality 



