ORTHOGENESIS 297 



moting its welfare. This idea was suggested to 

 paleontologists by the study of fossil organisms. 

 Koken, a geologist and paleontologist, made frequent 

 use of this argument. The point is well illustrated by 

 the gigantic reptiles found in cretaceous strata, whose 

 very size, weight and lack of agility became incom- 

 patible with their survival; likewise the exaggerated 

 dimensions of the Irish stag's antlers and the overde- 

 veloped and curved tusks of the mammoth led to the 

 extinction of these two races of animals. 



Overdevelopment of certain structures beyond the 

 limit of usefulness is observable, not only in extinct 

 species, but in modern animals as well. We men- 

 tioned elsewhere the overperfect protective coloura- 

 tion of the Kallima and the overdeveloped tusks of 

 the Babirussa. We could also mention, among other 

 examples, the eyes of certain crustaceans, located at 

 the end of exaggerated eyestalks. It seems as though 

 in these cases, development having once begun, had 

 continued through inertia in one given direction with- 

 out being able to stop after reaching the stage when 

 natural selection should have not only ceased to foster 

 it, but prevented it. 



The same may be true of characters which differ 

 from the point of view of usefulness, such as the di- 

 mensions and proportions of certain inactive struc- 

 tures, details of colouring, etc., which do not appear 

 accidentally, but show a tendency to develop in definite 



