18701882] HYATT AND COPE 345 



theory. This, I think, perhaps is largely due to the complete Letter 255 

 absorption of his mind in the contemplation of his subject : 

 this seems to lead him to be careless about the methods in 

 which it may be best explained. He has, however, a more 

 extended knowledge than I have, and has in many ways 

 a more powerful grasp of the subject, and for that very reason, 

 perhaps, is liable to run into extremes. You ask about the 

 skipping of the Zoea stage in fresh-\vater decapods : is this an 

 illustration of acceleration ? It most assuredly is, if accelera- 

 tion means anything at all. Again, another and more general 

 illustration would be, if, among the marine decapods, a series 

 could be formed in which the Zoea stage became less and less 

 important in the development, and was relegated to younger 

 and younger stages of the development, and finally dis- 

 appeared in those to which you refer. This is the usual way 

 in which the accelerated mode of development manifests 

 itself; though near the lowest or earliest occurring species 

 it is also to be looked for. Perhaps this to which you allude 

 is an illustration somewhat similar to the one which I have 

 spoken of in my series, 



a ab abc ae 



~~~ ad y 



which like "a d" comes from the earliest of a series, though I 

 should think from the entire skipping of the Zoea stage that 

 it must be, like " a e," the result of a long line of ancestors. In 

 fact, the essential point of our theory is, that characteristics 

 are ever inherited by the young at earlier periods than they 

 are assumed in due course of growth by the parents, and that 

 this must eventually lead to the extinction or skipping of 

 these characteristics altogether. . . . 



Such considerations as these and the fact that near the 

 heads of series or near the latest members of series, and not at 

 the beginning, were usually found the accelerated types, which 

 skipped lower characteristics and developed very suddenly to a 

 higher and more complex standpoint in structure, led both 

 Cope and [myself] into what may be a great error. I see 

 that it has led you at least into the difficulty of which you 

 very rightly complain, and which, I am sorry to see, has cost 

 you some of your valuable time. We presumed that because 

 characteristics were perpetually inherited at earlier stages, 



