3o8 



GENERAL PRINCIPLES 



etc., in which neither eggs nor spores occur. Still, in essence, 

 it is now generally accepted as true that all living things 

 originate from eggs, and in this statement is expressed one of 

 the most remarkable attributes of the living substance, that of 

 its continuitv. 



Fig. 178. Amoeba vespertilio, showing the structure of the protoplasm. The 

 outer layer is denser and more homogeneous, and is called ectoplasm. The 

 central part, called endoplasm, has the appearance of foam. (From Marshall 

 after Doflein.) 



672. Structure of Protoplasm. — Much has been learned con- 

 cerning the physical and chemical properties of protoplasm, 

 but even our best microscopes and most refined chemical 

 methods still leave much more to be determined. As seen 

 through the microscope the cytoplasm seems to consist of: (i) 

 a ground substance of a transparent, colorless, homogeneous 



