MARINE REPTILES 223 



many problems relating to the morphology, relationships, geologic range, 

 geographic range, probable habits, and ecological relations of each mem- 

 ber of each group. One phase of any problem for any member of a group 

 may well furnish a profitable subject for exhaustive investigation, but 

 the ultimate biological value of all sucli work depends largely upon the 

 extent to which it assists in an understanding of the processes involved 

 in the evolution of the organic world, and through this means helps to 

 interpret life in the broad sense. Viewed in this light, the marine 

 reptiles, together with the marine mammals, without regard to their posi- 

 tion in the scheme of classification, furnish a problem of peculiar interest, 

 which seems to the writer to be one of the large questions still before us 

 for solution. By reason of the peculiar environment in which marine 

 forms of all ages and all quarters of the earth's surface have lived, the 

 problem of their evolution is more sharply defined than in most groups, 

 an,d therefore perhaps more easily investigated. 



The significance of the changes which have taken place in the history 

 of the marine reptiles and mammals has been held by some to be rela- 

 tively slight in so far as the probability of their throwing light on the 

 problem of cause or mode of evolution is concerned, as the possibilities 

 of change or modification are narrowed in these forms by reason of the 

 peculiar environment. If the influence of selection be considered a 

 factor, it could work only in one direction, if worked at all. To some, 

 natural selection unaided does not seem in any way competent to account 

 for the rapid evolution through numerous stages shown by these reptiles ; 

 and the influence of the environment either through the direction of 

 mutations or through directing the mode of use of organs, and therefore 

 possibly the development of the animal, has been considered responsible 

 to a large extent for the tendency and extent of modification. 



The question whether the peculiar problem of aquatic adaptation, 

 especially as presented by the reptiles and mammals, is to aid us par- 

 ticularly in an understanding of evolutionary processes, and whether 

 these paleontologic series are by reason of the peculiar limitations of 

 environment especially significant, is yet to be definitely determined. 

 We need first of all a much fuller understanding of all the living and 

 extinct groups, and, following this, a much more exhaustive historical 

 study of the whole problem than has thus far been undertaken. 



