7 8 LIFE. 



matter from the fluid surrounding it, or is it formed from 

 within ? and which is the oldest part of the capsule, its 

 external or internal surface? If the new matter were 

 deposited upon the external surface, we should expect to 

 find that the membrane would become thicker and thicker 

 as the growth of the organism advanced, while the central 

 portion would remain unaltered. This, however, is not the 

 case ; on the contrary, we find that as growth proceeds, the 

 wall in most cases becomes considerably thinned. It is 

 clear, therefore, that the increase in size cannot be due to 

 deposition from without. The matter deposited upon the 

 inner surface of the capsule is always softer than its general 

 substance, and the external surface of old capsules is 

 cracked and ragged. 



In many of the algae this external surface serves as a 

 nidus for the development and growth of smaller algae a 

 fact which clearly shows it has ceased to be active, is under- 

 going disintegration, and becoming fitted for the pabulum 

 of other things, and is no longer capable of resisting the 

 action of external conditions. This is the oldest part of the 

 capsule which is now undergoing decay, and the small algae 

 are living in part upon the products thus produced. The 

 new material is added upon the inner surface of the capsule, 

 layer after layer, and where there are several layers the 

 innermost is the youngest and the outermost the oldest 

 portion of the structure. If this be so, it follows that the 

 inanimate material for the nourishment of these structures 

 must pass through the outer membrane, and be taken up by 

 the living matter within, which communicates to it the 

 same properties and powers which this living matter itself 



