290 PROCEEDINGS OF THE ACADEMY OF 



dently adaptive in their nature. This is part of the " natural selection" of 

 Darwin. 



That this law is subordinate to the one first propounded must, I think, be evi- 

 dent to any one who studies the assumed results of the workings of both, as 

 seen in the characters of genera. It is sufficiently well known that the essential 

 features of a majority of genera are not adaptive in their natures, and that 

 those of many others are so slightly so as to ofifer little ground for the suppo- 

 sition that the necessity has produced them. 



Both laws must be subordinate to that unknown force which determines 

 the direction of the great series. If a series of suppressions of the nervous 

 and circulatory systems of beings of common birth produced the " synthetic " 

 predecessors of the classes of vertebrata, the direction towards which the 

 highest advanced, or its ultimate type, can be only ascribed as yet to the 

 divine fiat. So far as we can see, there is no reason or law to produce a 

 preference for this direction above any other direction. 



If from these fixed bases descendants have attained to successive stations 

 on the same line of progress, in subordinate features of the nervous and cir- 

 culatory systems, constituting the " synthetic " predecessors of the orders ia 

 each class, the type finally reached seems to rest on n5 other basis than the 

 pleasure of the Almighty. 



/?. As affecting family characters. 



If from the single species generalizing a modern order we attempt to de- 

 duce synthetic predecessors of existing families, we find some difficulty, if we 

 attempt to see in these stages a uniform succession of progress. A sup- 

 pression of some features, and advance in others, in one and the same indi- 

 vidual up to the period of reproduction, would produce offspring divergent 

 from the start, and represent the relationship of families as we find them. 



y. As affecting generic characters. 



If the extremes of our series of genera were characterized by structures 

 particularly adapting them above all others to some cotemporary necessity of 

 existence, this second law, or Darwin's, might be regarded as primary. But 

 the writer's experience of comparative anatomy has led him to believe that 

 this is not the case, as expressed in Proposition IV. • 



This view has not been overlooked by Darwin, who, however, treats of it 

 very briefly, and appears to attach it to the theory of adaptations, or modifi- 

 cations for a physiological purpose. He says, Origin of Species, 388 (Amer. 

 Edit. 1860): " We may extend this view to whole families, or even classes. 

 The fore-limbs which served as legs in the parent species may become, by a 

 long course of modification, adapted in one descendant to act as hands, in 

 another as paddles, in another as wings; and on the above two principles, — 

 namely, of each successive modification supervening at a rather later age, and 

 being inherited at a correspondingly late age, — the fore-limbs in the em- 

 bryos of the several descendants of the parent species will still resemble each 

 other closely, for they will not have been modified. But in each individual 

 new species the embryonic fore-limbs will differ greatly from the fore-limbs 

 in the mature animal; the limbs in the latter having undergone much modi- 

 fication at a rather late period of life, and having thus been converted into 

 hands, paddles or wings." He then inclines to assign this change to the ne- 

 cessity of external circumstance. But such modification must be the same in 

 kind as others, which the same hypothesis must explain, and of which the 

 same author remarks (p. 382) : " We cannot, for instance, suppose that in the 

 embryos of the Vertebrata the peculiar loop-like course of the arteries near 

 the branchial slits are related to similar conditions in the young mammal, 

 which is nourished in the womb of its mother, in the egg of the bird which is 

 hatched in a nest, and in the spawn of a frog underwater. We have no more 



, [Oct. 



