i6o (16) 



approach to birds made by the reptiles Laelaps and 

 Megadactylus ; and the combination of characters of 

 the sub-orders of Cryptodire and Pleurodire Tortoises 

 in the Adocus of New Jersey. 



that modification to have taken place by a necessary progress from 

 more to less embryonic forms, from more to less generalized types, 

 within the limits of the period represented by the fossiliferous 

 rocks ; that it shows no evidence of such modification ; and as to 

 the nature of that modification, it yields no evidence whatsoever 

 that the earlier members of any long-continued group were more 

 generalized in structure than the later ones." 



Respecting this position, he says : " Thus far I have endeavored 

 to expand and enforce by fresh arguments, but not to modify in any 

 important respect, the ideas submitted to you on a former occasion. 

 But when I come to the propositions respecting progressive modi- 

 fication, it appears to me, with the help of the new light which has 

 broken from various quarters, that there is much ground for soften- 

 ing the somewhat Brutus-like severity with which I have dealt with 

 a doctrine for the truth of which I should have been glad enough 

 to be able to find a good foundation in 1862. So far indeed as the 

 Invei tebrata and the lower Vertebrata are concerned, the facts, and 

 the conclusions which are to be drawn from them, appear to me to 

 remain what they were. For anything that as yet appears to the con- 

 trary, the earliest known marsupials may have been as highly organ- 

 ized as their living congeners ; the Permian lizards show no signs 

 of inferiority to those of the present day ; the labyrinthodonts can- 

 not be placed below the living salamander and triton ; the Devonian 

 ganoids are closely related to polypterus and lepidosiren." 



To this it may be replied : I. The scale of progression of the 

 Vertebrata is measured by the conditions ef the circulatory system, 

 and in some measure by the nervous, and not by the osseous : 

 tested by this scale, there has been successional complication of 

 structure among Vertebrata in time. 2. The question with the 

 evolutionist is, not what types have persisted to the present day, 

 but the order in which types appeared in time. 3. The Marsupials, 

 Permian saurians, labyrinthodonts and Devonian ganoids are re- 

 markably generalized groups, and predecessors of types widely 

 separated in the present period. 4. Professor Huxley adduces 



