10 GENERAL EVOLUTION. 



their first horn, which is unbranched and small, or a " spike," A 

 genus of deer inhabiting South America never develops anything 

 else. To take a character of higher grade : tbe exogenous plants 

 usually present net- veined leaves, but the first pair, or those of 

 the plumule, are of much simpler structure, being often parallel- 

 veined ; for example, the cucumbers and squashes. Now, the en- 

 dogens usually produce nothing else than parallel-veined leaves, and 

 no case is known where a plant bearing this type of leaf exhibits 

 the net-veined type as its earliest growth. 



But what do these facts mean ? As in growth the genus char- 

 acters usually appear last, I will suppose a case where one genus 

 represents truly, or is identical with, the incomplete stage of an- 

 other one. 



In A we have four species whose growth attains a given point, 

 a certain number of stages having been passed prior to its termi- 



nation, or maturity. In B we have an- 



^^^ A other series of four (the number a mat- 

 ter of no importance), which, during the 

 period of growth, can not be distin- 

 h guished by any common, i. e., generic 

 ■ character, from the individuals of group 



■ A, but whose growth has only attained 



^^' ' to a point short of that reached by those 



of group A at maturity. Here we have a parallelism, but no true 

 evidence of descent. But if we now find a set of individuals be- 

 longing to one species (or, still better, the individuals of a single 

 brood), and therefore held to have had a common origin or parent- 

 age, which present differences among themselves of the cliaracter 

 in question, we have gained a point. "VVe know in this case that 

 the individuals, a, have attained to the completeness of character 

 presented by group A, while others, b, of the same parentage have 

 only attained to the structure of those of group B. It is perfectly 

 obvious that the individuals of the first part of the family have 

 grown further, and, therefore, in one sense faster, than those of 

 group b. If the parents were like the individuals of the more 

 completely grown, then the offspring which did not attain that 

 completeness may be said to have been retarded in their devel- 

 opment. If, on the other liand, the parents were like those less 

 fully grown, then the offspring which have added something 

 have been accelerated in their development. I claim that a con- 

 sideration of the uniformity of nature's processes, or inductive 



