1 88 MODERN IDEAS OF EVOLUTION 



or white of egg which is otherwise named proto 

 plasm is a very complicated substance chemically, 

 and in its molecular arrangements, and when endowed 

 with life, it presents properties altogether inscrutable. 

 It is easy to say that the protoplasm of an egg or of 

 some humble animalcule or microscopic embryo is 

 little more than a mass of structureless jelly, yet 

 in the case of the embryo a microscopic dot of this 

 apparently structureless jelly must contain all the 

 parts of, say, a bird or a mammal ; but how we may 

 Nnever know, and certainly cannot yet comprehend. 



There are minute animalcules belonging to the 

 group of flagellate infusoria, some of which, under 

 ordinary microscopic powers, appear merely as moving 

 specks, and show their actual structures only under 

 the highest powers ; yet these animals can be seen to 

 have an outer skin and an inner mass, to have pul 

 sating sacs and reproductive organs, and threadlike 

 flagella wherewith to swim. Their eggs are, of course, 

 much smaller than themselves, so much so that some 

 of them are probably invisible under the highest 

 powers employed. Each of them is potentially an 

 animal, with all its parts represented structurally in 

 the same way. 



Nor need we wonder at this. It has been calcu 

 lated that a speck scarcely visible under the most 

 powerful microscope may contain two million four 

 hundred thousand molecules of protoplasm. If each 

 of these molecules were a brick, there would be enough 





