THE EVIDENCE FROM DEVELOPMENT. 193 



to the special, thus declares a great truth of nature. Modern biology 

 appears provided with a host of witnesses to the truth of that axiom, 

 and supplies a reason for the likeness by assuming similarity of descent 

 from lower life as the explanation of those common and general 

 beginnings from which the special and varied forms of animals and 

 plants are evolved every hour around us. The axiom that the deve- 

 lopment of the individual (ontogenesis] is the rapid shifting or pano- 

 ramic recapitulation of the development of the species (phylogenesis], 

 is now regarded in biology as the keynote of the whole study of 

 animal and plant formation. If we find, for instance, that the frog in 

 its development is firstly a fish, then a tailed amphibian or newt, and, 

 last of all, a tailless, air-breathing frog, we see in such a panoramic 

 succession of changes constituting the development of the individual 

 the evolution and development of the frog race. We read such a 

 history as showing us clearly enough that the frogs have been evolved 

 from some ancient fish-stock, that this fish ancestor became through suc- 

 ceeding modifications a tailed, newt-like amphibian, and finally, that the 

 newt in turn became the higher frog. Most reasonable is the supposi- 

 tion and belief that, if the living hosts have descended from common 

 ancestors, the appearance of ancestral features in their development is 

 a most natural expectation and a highly natural law of life. That trans- 

 mission from parent to offspring of hereditary features, so familiar to us 

 in human existence the reproduction of family features by the suc- 

 cessive descendants of the family stock is, in truth, but the repeti- 

 tion in higher life of the likenesses to its ancient ancestry we see in 

 the developing frog. On such grounds, we may attempt successfully 

 to explain the mysteries of development ; and on such a principle, we 

 may note in passing, it is easy to see how important a guide to the 

 classification and arrangement of living beings their development 

 affords. If those animals which are descended from a common 

 ancestry resemble each other in their development, such resem- 

 blances may be held to represent the truest of those blood relation- 

 ships which it is the business and aim of classification to express. 



The chronicle of the development of animal life is, however, not 

 completed when the earliest changes seen in the formation of the 

 animal frames have been noted. Long after the common and earliest 

 stages, described in the last chapter, have been completed, there 

 may be produced before us marvellous resemblances and likenesses be- 

 tween animals which, when adult, would seem to possess no community 

 either of origin or of other relationship. It is to these later changes 

 in the animal form that we now purpose to direct attention. The 

 history of those changes which more immediately precede the 

 assumption of adult life, affords as valuable evidence of the evolution 

 of species, as does the chronicle of the very beginnings of existence. 

 It is only needful to point out at the commencement of such a study, 



o 



