I9 6 MODE OF FORMATION 



branch or process which grows exactly like the first The 

 process thus forme'd may extend a long way from its point 

 of origin where it often breaks off. It continues to grow at 

 the distal extremity and occasionally branches in the 

 manner already referred to. At the growing point the 

 membrane is thinnest and the bioplasm is most deeply 

 tinted by the carmine fluid. PI. II, fig. 3. 



Now, let us inquire how an organism so simple nourishes 

 itself? The materials for its growth and nourishment are 

 certain inanimate matters (solids and gases) which are dis- 

 solved in the fluid in which the organism floats. These 

 materials must pass into its structure and become part of it. 

 That which is inanimate must become incorporated with 

 and assume the properties of the living matter. 



In the increase of the simple spore, then, how is the 

 new matter produced ? Does it take place by deposition 

 upon the external surface of the investing membrane, or is 

 the new matter produced by the soft formless matter in the 

 interior ? To put the question still more simply, Is the 

 capsule, the so-called cell-wall, formed by deposition of 

 matter from the fluid in contact with its external surface, 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, how- 

 ever, is not the case ; on the contrary, we find that as 

 growth proceeds, the wall in most cases becomes con- 

 siderably thinned. It is clear, therefore, that the increase 

 in size cannot be due to deposition from without. When 



