88 THE EVOLUTION OF SEX. 



cular change or metabolism. On the one hand, more or less 

 simple dead matter or food passes into life by a series of 

 assimilative ascending changes, with each of which it becomes 

 molecularly more complex and unstable. On the other hand, 

 the resulting protoplasm is continually breaking down into more 

 and more simple compounds, and finally into waste products. 

 The ascending, synthetic, constructive series of changes are 

 termed "anabolic;" and the descending, disruptic series, "kata- 

 bolic." Both processes may be manifold, and the predominance 

 of a particular series of anabolic or katabolic changes implies 

 the specialisation of the cell. The upper figure (a) represents 

 the complex unstable protoplasm as if occupying the summit of 

 a double flight of steps ; it is formed up the anabolic steps, it 

 breaks up and descends by the katabolic. The lower figure (b) 

 is a projection of the other, its convergent and divergent lines 

 serving to represent the various special lines of anabolism and 

 katabolism respectively, and the definite component substances 

 ("anastates" and " katastates ") which it is the task of the 

 chemical physiologist to isolate and interpret (see pp. 122-4). 



Protospongia^ a colonial infusorian, showing the difference bet^^'een 

 outer and inner cells. — From Saville Kent. 



§ 5. Protozoa and Metazoa. — It has been emphasised above 

 that every multicellular organism, reproduced in the ordinary 

 way, starts from a fertilised ovum, from what may be fairly 

 called a single cell. Sponge, butterfly, bird, and whale start at 



