72 Evolution and Adaptaton 
two, three years, etc., that it does so because its ancestors 
lived one year, two years, three years, etc.? The descent 
theory is correct so far as it maintains that older, simpler 
forms have been the forefathers of later complicated forms. 
In this case the resemblance of the older, simpler forms to 
the embryos of later forms is explained without assuming 
any law of inheritance whatsoever. The same resemblance 
between the older and simpler adult forms, and the present 
embryonic forms would even remain intelligible were there no 
relation at all between them.” 
Interesting and important as is this idea of His, it will not, 
I think, be considered by most embryologists as giving an 
adequate explanation of many facts that we now possess. It 
expresses, no doubt, a part of the truth but not the whole 
truth. 
We come now to a consideration of certain recently 
ascertained facts that put, as I shall try to show, the whole 
question of embryonic repetition in a new light. 
A minute and accurate study of the early stages of 
division or cleavage of the egg of annelids has shown a 
remarkable agreement throughout the group. The work of 
E. B. Wilson on nereis, and on a number of other forms, as 
well as the subsequent work of Mead, Child, and Treadwell 
on other annelids, has shown resemblances in a large number 
of details, involving some very complicated processes.! 
Not only is the same method of cleavage found in most 
annelids, but the same identical form of division is also pres- 
ent in many of the mollusks, as shown especially by the work 
of Conklin, Lillie, and Holmes. This resemblance has been 
discussed at some length by those who have worked out these 
results in the two groups. The general conclusion reached 
by them is that the only possible interpretation of the 
1 On the other hand it should not pass unnoticed that Eisigh as shown in one 
form (in which, however, the eggs are under special conditions being closely 
packed together) that the usual type of cleavage is altered. 
