242 THOMAS DWIGHT ON 



The Tjipe. — The study of this question, absolutely independent of the point of view, 

 brings more and more vividly before my mind the old idea of the archetype vertebra. 

 There is no denying that the costal elements by their greater or less development are the 

 cause of the immense majority of the variations. Oi-iginally this conception implied a 

 plan ; now it is tacitly admitted by all. The paragraph at the head of this paper is 

 the opening one of that masterpiece of destructive criticism, Herbert Spencer's review of 

 Owen's Archetype Skeleton. Certainly the extravagances of the dreamers who made 

 science ridiculous were easy prey ; but though it was not hard to dispose of any or all pre- 

 cise interpretations of the archetype skeleton, the idea of plan remains. Spencer, after 

 demolishing Owen, tried as a substitute theory that of accumulated modifications ; but it 

 is far from satisfactory. One may think Spencer had this in mind in the first sentence of 

 the paragraph above quoted. Indeed he points out the shortcomings of his own theory 

 with a rare frankness : " But, it may be replied, this hypothesis does not explain all the 

 facts. It does not tell us why a bone whose function in a given animal requires it to be 

 solid, is formed not of a single piece, but by the coalescence of several pieces which in 

 other creatures are separate : it does not account for the frequent manifestations of unity 

 of plan in defiance of teleological requirements. This is quite true." The idea of plan 

 is not easy to get rid of. The mind of man craves it. If there be nothing but absurdity 

 in the idea of a type vertebra, how is it that the actual thing, not imaginary amphfications 

 of it, holds its own so persistently ? Let those who find a sufficient answer in " heredity " 

 tell us how the vertebral system became so securely intrenched from the time of the first 

 appearance of vertebrates that it has never been dislodged. 



Beyond question, as was intimated above, one reason of the great success of 

 Rosenberg's theory has been that it fitted in so perfectly with the doctrine of descent by 

 gradual modifications. It has, unfortunately for science, become too much the custom to 

 make everything square with this doctrine. If a certain occasional feature shows a ten- 

 dency opposite to the course of phylogenesis, it is too often interpreted as necessarily a 

 step in the direction of future modifications. This is said of undeveloped 1st, 11th and 

 12th ribs in man, without regard to the fact that such an abbreviated thorax could hardly 

 be very satisfactory. 



In this spirit Fiirbringer ('79, p. 388) objects to v. Jhering's belief in inter- and exca- 

 lation of vertebrae because either this theory has consequences that are in contradiction 

 with the descent theory and therefore with the task of scientific morphology, or else it is a 

 non-comprehensive theory of little value. There is at last some protest against the dog- 

 matism that requires all phenomena to be accounted for in accordance with a certain 

 theory. Thus Kohlbrugge ('97, p. 14) : " I consider all so-called atavistic variations as 

 neutral in respect to the past or future type of the race, and occasioned either by varia- 



