Facts and Factors of Development 9 



(c) Reproduction, or the capacity of organisms to give rise to 

 new organisms, of cells to give rise to other cells, and of parts of 

 cells to give rise to similar parts by the process of division. 



(d) Irritability, or the capacity of receiving and responding to 

 impinging energies, or stimuli, in a manner which is usually, but 

 not invariably, adaptive or useful. 



Memb 



FlG. 2. A NEARLY RlPE HUMAN OVUM IN THE LlVING CONDITION. The 



ovum is surrounded by a series of follicle cells (FC) inside of which is the 

 clear membrane (Memb.) and within this is the ovum proper containing 

 yolk granules (Y) and a nucleus (N) embedded in a clear mass of proto- 

 plasm. Magnified 500 diameters (x 500). (From O. Hertwig.) B, two 

 human spermatozoa drawn to about the same scale of magnification. 

 (After G. Retzius.) 



