Chap. X."] GROUPS OF ALLIED SPECIES. 283 



longer perhaps in many ctses than the time required for the accu- 

 mulation of each formation. These intervals will have given time 

 for the multiplication of species from some one parent-form ; ar.d in 

 the succeeding formation, such groups or species will appear as if 

 suddenly created. 



I may here recall a remark formerly made, namely, that it might 

 require a long succession of ages to adapt an organism to some new 

 and peculiar line of life, for instance, to fly through the air ; and 

 consequently that the transitional forms would often long remain 

 confined to some one region ; but that, when this adaptation had 

 once been effected, and a few species had thus acquired a great 

 advantage over other organisms, a comparatively short time would 

 be necessary to produce many divergent forms, which would spread 

 rapidly and widely throughout the world. Professor Pictet, in his 

 •excellent Eeview of this work, in commenting on early transitional 

 forms, and taking birds as an illustration, cannot see how the suc- 

 cessive modifications of the anterior limbs of a supposed prototype 

 could possibly have been of any advantage. But look at the 

 (penguins of the Southern Ocean ; have not these birds their front 

 limbs in this precise intermediate state of " neither true arms nor 

 true wings " ? Yet these birds hold their place victoriously in the 

 battle for life ; for they exist in infinite numbers and of many kinds. 

 I do not suppose that we here see the real transitional grades through 

 which the wings of birds have passed ; but what special difficulty is 

 there in believing that it might profit the modified descendants of 

 the penguin, first to become enabled to flap along the surface of the 

 sea like the logger-headed duck, and ultimately to rise from its 

 surface and glide through the air? 



1 will now give a few examples to illustrate the foregoing remarks, 

 .and to show how liable we are to error in supposing that whole 

 groups of species have suddenly been produced. Even in so short 

 an interval as that between the first and second editions of Pictet's 

 great work on Palaeontology, published in 1844-46 and in 1853-57, 

 the conclusions on the first appearance and disappearance of several 

 groups of animals have been considerably modified ; and a third 

 edition would require still further changes. I may recall the well- 

 known fact that in geological treatises, published not many years 

 ago, mammals were always spoken of as having abruptly come in 

 at the commencement of the tertiary series. And now one of 

 the richest known accumulations of fossil mammals belongs to the 

 middle of the secondary series ; and true mammals hare been dis- 

 covered in the new red sandstone at nearly the commencement oi 

 ithis great series. Cuvier used to urge that no inonKey occurred in 



