Embryology 333 



the germ cell ; just the same as is done by the embryo fowl 

 or some other higher forms, up to that stage of develop- 

 ment. The difference is that after those changes the simpler 

 animal comes to the end of its growth energy; stops, and 

 ripens so to speak, and advances no further in development ; 

 while the more highly endowed animal at the same stage has 

 only begun its growth; and it pushes on, and adds its 

 acquisitions in more and more complex forms, until the one 

 first considered is entirely lost to view. We find mature 

 creatures of one cell, of four, eight, sixteen, thirty-two, 

 sixty-four, and so on, indefinitely and less regularly, ac- 

 cording to the number of times the germ cell's descendants 

 divide. But every creature of a large number of cells, must 

 reach that growth by evolution through simpler forms which 

 resemble those of some creatures of smaller cell number. 



The striking parallelism of this series of developing 

 forms, with that other series revealed by geological chro- 

 nology, is evident and fascinating. And it induces reflec- 

 tion upon the other parallel series of present living creatures 

 whose mature forms may be arranged in series so as to 

 nearly coincide. 



There is seen a revelation of resemblance of the complex 

 living creature to the simpler lower ones, and again to the 

 old and extinct ones. These immature embryological forms 

 are recognized as repetitions of form of an old, and some- 

 times of an extinct, geological species, and again are seen 

 as approximations to existing surviving lower species of 

 similar class. 



The resemblance however is not found to be always 

 exactly referable to the living lower organisms. Nor is it 



