168 



BIOLOGY: GENERAL AND MEDICAL 



reached, most of the higher animals cease to grow ancf 

 their cells cease to multiply 



Unrestricted powers of multiplication are indispensable 



FIG. 67. Sporulation. Developing stages of Coccidium ovifonne. 1, Young 

 intracellular organism, somewhat elongated; 2, an epithelial cell containing 

 two young organisms, undifferentiated in type; against the surface of the 

 larger organism is a disc of eosin-staining substance; 3, 4, 5, stages in the 

 development of the schizont; 6, merozoites as seen in stained smears; 7, merozoites 

 arranged in a rosette, about the restkorper. (From drawings made with camera 

 lucida, Zeiss comp., ocular No. 4, 1/12 homogeneous immersion.) (After 

 Tysser.) 



FIG. 68. Budding yeast cells (Saccharomyces cerevisiae), showing four 

 successive stages manifested by the nuclear apparatus. The large pale sphere 

 is the nuclear vacuole, the small dark sphere the nucleolus. 



to the lowly forms of life as the sole means of perpetu- 

 ating their kind. But among the metazoan animals 

 where the cells are but units in a complex structure, 

 little is to be gained by the indefinite growth of the 



