48 METAMOEPHOSES OF MAN 



here an excreting canal, and the earliest traces of a 

 secreting organ or gland. These primitive lobules 

 increase in number, and divide and subdivide, until 

 at last that huge bile-secreting organ, the liver, is 

 completely formed. All the other glands, the lungs, 

 &c, are formed in an exactly similar manner. Hence 

 it is very clear that none of these organs exist prior 

 to their appearance. '<■ ■ . 



Thus we see the developmental force first exhibiting 

 itself within a special centre, — the germinal area ; then 

 in three secondary centres, — the three layers; and 

 finally, in several different centres, as it helps to 

 complete the various structures which at first were of 

 a simple character. But epigenesis exhibits itself 

 especially in laying the foundation of the embryo 

 itself and of all its structures. 



Each organ being at first roughly formed as it 

 were, and exceedingly small, must eventually increase 

 in size. Then, the purely epigenetic phenomena are 

 followed by those of evolution, which present them- 

 selves under two principal forms. 



An organ may grow without having its form or 

 structure changed in any particular. The envelopes 

 of the egg, the amnion of the embryo, and almost all 

 the apparatus of the child, afford us numerous proofs 

 of this. But in some cases organs must change their 

 form, proportions, and size, ere they undergo this the 

 most simple process of evolution. Now, in order to 

 concentrate our attention, we shall here confine our- 

 selves to two facts borrowed from human embryogeny. 

 In man, the arms, when they first appear, are like a pair 

 of -little rounded paddles placed near the centre of the 

 body, and the tail, which is now quite as long as in other 



