LECTURE XVI. 



453 



an ideal gap, but in tlie establishment of real intermediate 

 forms, which, by gradual unfolding and transformation, de- 

 velope themselves from lower forms and approach the higher — 

 an approximation which here succeeded only up to a certain 

 point, but is accomplished in the more perfect forms. 



But, we are told, these -intermediate forms certainly fill up 

 the gap between great divisions, but the minuter transitions, 

 which might teach us the process of this transformation, are 

 entirely wanting. We ought to be able to trace these transi- 

 tions step by step, both in living and fossil species. As regards 

 living species, this would not be very difficult. Place side by 

 side the skulls of the various species of the genus Gebus, and 

 see whether you cannot establish a perfect series of minute 

 changes in form, as in dogs or cattle. The transitions are 

 then rendered as evident as they are in a series of Orang skulls 

 of different ages in the extreme forms of the round young 

 head, and the long extended head of the old orang. With 

 regard to fossil skulls, need I instance those of bears ? The 

 great cave-bear, with its prominent brow-ridge and its convex 

 elevations on the forehead, is certainly, as A. Wagner has 

 shown, a distinct species, just as our present brown bear ; but 

 are there no intermediate forms, such as the Ursus arctoideus, 

 which, though it attains the size of the cavern-bear, has 

 neither its frontal eminences, nor such thick bones ? then 

 there is the JJrsus Leodiensis, which is smaller than the cavern- 

 bear, aud shows no such frontal eminences ; there is also the 

 Ursus priscus, smaller than the cave-bear, but resembUng in 

 profile the still smaller brown bear; and finally the brown 

 bears found in the caverns of Switzerland, the skulls of which 

 show a gigantic size, approaching that of the cave-bear. All 

 these transitional forms are very rare. We possess only a few 

 specimens of each, whilst skulls of cavern- and of brown-bears 

 are collected by hundreds. The large, savage, and formidable 

 cavern bear corresponds with the conditions which surrounded 

 him, in the same manner as the living brown bear corresponds 

 with existing conditions. The transition from the cave-period to 

 the present, perhaps, took place within a comparatively short 

 time, consequently the transitional forms, indicating the raceless 

 oscillations between two fixed types, are very rare, compared 



