FAUNA AND FLORA OF THE SEA BOTTOM. 1 235 



extent and frequency; in other cases, one is of much greater abundance than 

 the other, though their range of distribution is practically the same; in others 

 still, one has a much more restricted range than the other. As instances of the 

 last condition we may mention the two common starfishes, Asterias forbesi 

 and A. vulgaris (fig. 20, 21), or the two chestnut shells, Astarte castanea and 

 A. undata. In each of these examples the two related species overlap through- 

 out a part of their range, but the range of one is more restricted than that of 

 the other. 



Whether or not the specific differentiation preceded or followed such a 

 change of habitat is not even suggested by any of the facts which we have 

 encountered. Who can say, for example, whether the tendency to restrict 

 itself to muddy bottoms preceded or followed the differentiation of the amphipod 

 crustacean Ampelisca macrocephala as a species distinct from A. spinipes? Yet 

 this is the kind of data with which we have to deal. Nevertheless, the bare 

 fact that various closely related species do show decidedly different distribution 

 patterns is one of great interest, for it shows that the slight morphological differ- 

 ences by which the species are distinguished from one another are oftentimes 

 correlated with marked physiological differences, sufficient to adapt the two 

 to differing habitats. Thus the assertion so often made that the slight struc- 

 tural differences by which we distinguish one species from another are com- 

 monly of no conceivable utility, and therefore can never have arisen through 

 the action of natural selection, loses much of its force. While it may be true 

 that these slight structural differences in themselves can play no significant 

 role in the life of the organisms concerned, it is likewise evident that there are 

 certain correlative physiological changes sufficient to adapt the organisms to 

 somewhat different modes of life. That natural selection has been the con- 

 trolling factor in the origination and perpetuation of such specific differences, 

 whether morphological or physiological, is far from certain. But that the 

 characters concerned are in most cases too insignificant to be of selective value 

 is also far from certain. 



To the reader who would demand an exact economic equivalent for the 

 labor and money here expended our answer must be a more general one. 

 Science and industry move together. Industry is helpless without the aid of 

 science, and the greatest industrial progress is at present being made by those 

 countries which realize this fact most fully. But science can never prosper if 

 forced to play the role of a servant. She must be free to pursue her own ends 

 without being halted at every step by the challenge: cui bono9 The attempt 

 to restrict our scientific experts to problems of obvious economic importance 

 would be equivalent to depriving ourselves of their services altogether. It 

 is to-day accepted as a commonplace that all the great discoveries of practical 

 value have rested ultimately upon principles first brought to light by the student 



