216 THE INFLOENCE OF INANIMATE SDEROUNDINGS. 



adapted to resist pressure or impact in a certain direction. In 

 the total absence of any exact knowledge on this point, we may 

 set such cases aside and address ourselves to the investigation of 

 those where the mechanical influence of a constant current is, 

 by itself, of manifest importance in modifying the growth of 

 fixed or sedentary animals. 



In this respect the Coral animals are of predominant im- 

 portance, for in all the specie s, large and small, the tendency 

 is conspicuously manifest — and in the individual Polyps as well 

 as in the whole mass — to exert the vigour and direction of 

 their growth to counteract the strength and direction of the 

 current or pressure they may be exposed to. On the other hand, 

 the question as to the way in which the growth of Corals maybe 

 affected or modified by external circumstances is of the greatest 

 importance with reference to Darwin's well-known theories as 

 to the origin and formation of coral reefs. We should have no 

 occasion to give much attention to the phenomena I allude to 

 if they either simply availed to confirm Darwin's views, or, on 

 the other hand, in no way affected them; but as they elucidate 

 in detail the same views, antagonistic to Darwin's, which 

 I have gradually arrived at after a careful investigation of the 

 whole mode of growth of coral reefs in general, I feel called 

 upon here to describe them fully. The high authority which 

 every opinion expressed by Darwin has, and always must have, 

 in my estimation, would of itself justify our giving our best 

 attention to a thorough investigation of any qiiestion bearing 

 upon them ; and it seems all the more permissible in this in- 

 stance, because the easy application of Darwin's theories of 

 coral-reef formation, their extreme simplicity, and partly also 

 the great interest which has always been excited in the popular 

 mind by the processes of coral growth, have made them almost 

 universally known to the geologist as a convenient hypothesis, 

 and to the layman as one easily grasjped and understood. In 

 the following disquisition I shall proceed from special cases, and 

 afterwards discuss the more general question. 



A. The influence on growing corals of a constant current 

 produced by other animals. — So long ago as the year 1837 

 Stimpson described a small crab, under the name of Hapalo- 



