224 SPECIES NOT 



How can we explain these several facts in em- 

 bryology: 1st. The very general, but not uni- 

 versal difference in structure, between the embryo 

 and the adult. 



It is difficult to understand how this could 

 have been otherwise, as far as external appear- 

 ances, the worst of all guides in the matter, is 

 concerned. The embryo is the germ only, of the 

 future animal. It is a structure as yet unfin- 

 ished, and of course appears different. Look at 

 a caterpillar. How unlike a butterfly ! Yet 

 -when it makes its final change into a pupa, you 

 can trace in the pupa-case all the organs, 

 wings, legs, antennas, eyes, of the future insect! 

 Break the pupa into two parts, and you will 

 find it hollow, containing a fluid. Still how 

 unlike a butterfly. In a fortnight or more, if 

 left under the circumstances which the species 

 requires, your pupa splits, and out comes a 

 perfect insect! Who will say that at least the 

 pupa did not foreshadow the insect, and yet 

 how different? 



2nd. "Parts in the same individual embryo, 

 which ultimately become very unlike, and serve 

 for divers purposes, being at this early period 

 alike." This question has been answered before. 

 If the embryo has to exist as a fish, it is pro- 

 vided with branchiae in early life, as the reptile 

 is. The visceral arches in the embryo of the 

 human frame are in no way analogous with the 

 branchiae of fish, inasmuch as they are converted 

 into the bones of the face. 



