STUDIES IN ANIMAL LIFE. 23 



boys will pelt, anatomists dissect, and Frenchmen 

 eat. From the starting-point of a single cell this 

 is the course taken : the cell divides itself into two, 

 the two become four, the four eight, and so on, till 

 a mass of cells is formed not unlike the shape of 

 a mulberry. This mulberry-mass then becomes a 

 sac, with double envelopes or walls ; the inner wall, 

 turned toward the yelk, or food, becomes the assim- 

 ilating surface for the whole ; the outer wall, turned 

 toward the surrounding medium, becomes the sur- 

 face which is to bring frog and philosopher into 

 contact and relation with the external world the 

 Non-Ego, as the philosopher in after life will call it. 

 Here we perceive the first grand " setting apart," or 

 differentiation, has taken place ; the embryo having 

 an assimilating surface, which has little to do with 

 the external world, and a sensitive, contractile sur- 

 face, which has little to do with the preparation and 

 transport of food. The embryo is no longer a mass 

 of similar cells ; it is already become dissimilar, dif- 

 ferent, as respects its inner and outer envelope. 

 But these envelopes are at present uniform; one 

 part of each is exactly like the rest. Let us, there- 

 fore, follow the history of Development, and we 

 shall find that the inner wall gradually becomes un- 

 like itself in various parts, and that certain organs, 

 constituting a very complex apparatus of Digestion, 

 Secretion, and Excretion, are all one by one wrought 

 out of it by a series of metamorphoses or differentia- 

 tions. The inner wall thus passes from a simple 



