THEORY OF SEX — ITS NATURE AND ORIGIN. 



121 



amoeba. He is now in a position to recognise that the chapters 

 in the hfe-history of the simplest forms are, as it were, prophecies 

 of each of his three groups. Before final differentiation has 

 taken place, the organisms pass through a cycle of phases, one 

 of which is accented by each of the different groups of the 

 Protozoa. Thus an infusorian has its encysted chapter, a 

 gregarine its amoeboid stage, and a rhizopod may begin as a 

 mobile ciliated spore ; for each group, while accenting one 

 phase of the cycle, retains embryonic reminiscences of the 

 others. 



Diagram of the Cell-cycle, — of encysted, ciliated, and amtuboid 

 phases. I., II., III., in Protozoa; IV., ovum and sperm of 

 fern prothallus ; V., encysted, ciliated, and anujeboid 

 animal cells; VI., ciliated animal cell pathologically 

 becoming amccboid ; VII., sperm and amoeboid sperm; 

 VIII., ama-boid and encj-sted ovum. — From Geddes. 



A conviction that the triple division really meant much 

 would grow in our student's mind, if he passed from the 

 Protozoa to the cells which compose higher animals. There he 

 would find active ciliated cells in most of the classes, from the 

 ■Siated chambers which lash the water into a sponge, to the 

 cells lining the air passages in man ; passive encysted cells 

 would be illustrated in some forms of connective, fatty, and 



