sept. 1910.] FUJII.-SOME REMARKS ON THE CRET. FLORA ETC. 217 



limits of their longevity, admitting that the environment 

 remained unchanged in the meantime, is often expressed. It 

 sounds pleasingly, and we may take shelter under it, in case 

 we failed to explain the cause of extinction of organic species 

 otherwise ; but it may or may not have some truth in* itself. 



This extinction of species with old age may prove to have a 

 certain direct or indirect relation with the geological periods of 

 mutation (De Yries, Mutationstheorie, 1903.). In saying ' it 

 may have some truth in it,' one must recognize that the species 

 is an aggregate of individuals which have been materially con- 

 nected once in their development history with the common 

 stock by the germinal cells from which they arose, thus the 

 effect of their old ages which will accumulate through genera-, 

 tions being in some way carried on to their descendants. 



But the validity of this view must be on one hand carefully 

 tested by the considerations of paleontological data, and on 

 the other hand be supported by experimental facts if possible, 

 to show that organisms, after a long series of generations, 

 actually produce weaker individuals, before any change of con- 

 stitution of the medium or environments occurred. 



Rosa (Daniel Rosa, 1899 ; German Edition 1903) speaks of 

 the dying-out of the species as due to the progressive reduction 

 of variations in the course of generations and this reduction 

 of the variations as the result of the progressive reduction 

 of variablity of the species. 



Cope (1896), in demonstrating his ' law of the unspecializ- 

 ed,' states that the specialized types gradually die out, as it is 

 incapable of variation, and new types arise from the unspecialized 

 members far behind in the series. 



But what is specially maintained by these two authors is 

 about the cause of extinction of a certain line of descent, or of 

 dying out of a branch of the phylogenetic tree, and not about 

 the cause of extinction of individual species with which I have 

 been hitherto concerned. 



At the same time, however, Cope as well as Rosa speak 

 clearly of the incapability of the existence of specialized type at 



