RIB VARIATION IN CARDIUM. 



FRANK COLLINS BAKER. 



Contents. 



I. Introduction. II. Material. III. Method of obtaining; 

 quantitative data. IV. Discussion of data. Cardium robustum. 

 Cardium isocardia. Cardium muricaium. V. Comparison of 

 the three species. 



I. Introduction. 



At the present time biologists and zoologists are paying 

 marked attention to the study of the laws of variation, such 

 studies having a strong bearing upon the origin of species. The 

 results of such studies will be of little value, however, unless 

 great care is taken in recording the exact locality from which 

 the material came. And likewise the results will be //// unless 

 the material studied is of such a quantity as to form a good basis 

 for a quantitative examination. It frequently happens that a 

 careful study of the variation of a certain species is rendered 

 valueless because the working material has been too limited in 



That the time expended in such study is well spent is clearly 

 shown by the following statement made by the late Prof. Edward 

 D. Cope. 1 



" So soon as sufficient material becomes available, the zoolo- 

 gist can make that kind of research into the permanency "and * 

 variability of the characters of species which characterizes the 

 exact stage of the science. It is on such study that all useful 

 conclusions as to the origin of species depends. It is not the 

 orderly relation of species and genera to each other that demon- 

 strates the truth of the hypothesis of the derivation of the 



