404 Mr. J. S. Gardiner on the Distribution 



are of importance in distributing species and genera from shore 

 to shore, from one littoral zone to another. It may, perhaps, 

 clear the ground if I suggest, in the first place, that we confine 

 our attention to such animals as belong to the benthos, the 

 sedentary, creeping, and burrowing fauna of the bottom. Here 

 we can deal for the most part with well-defined groups, all 

 of true benthos forms, any extensive wandering of the species 

 or genera of which must be due to the distribution of their 

 pelagic larvje, direct migration of the adults of littoral forms 

 across or beneath the deep-sea being quite exceptional. 



It appears to me that it would be a profitable and perfectly 

 legitimate question to consider what would be the fauna of a 

 bank or the littoral zone of an island upheaved halfway 

 between Land's End and Bermuda after 100 or 1000 years ! 

 We should want to know accurately a great number of factors 

 to answer such a question. First, we make inquiry as to 

 what currents would lave our bank and what would be the 

 temperature of the water around it at each and every season 

 of the year. In the case cited, the only current of importance 

 would be the Gulf Stream, and it would be an easy matter to 

 ascertain or calculate the temperatures. We then carefully 

 examine the topography of the ocean-basin and the surrounding 

 coasts to see from whence it could with such currents become 

 populated. If our bank arises, as it would, from 2000 fathoms 

 and there are no shoals of less than 1000 or, possibly, 500 

 fathoms, our task would be simplified, and we would at once 

 commence an examination into the littoral fauna of the 

 Bermuda reefs and slopes. If, however, we found, as is 

 quite possible, ridges or isolated banks arising to a less 

 depth from the surface — I should suppose the vertical distri- 

 bution of the littoral fauna to continue down to about 250 

 fathoms, the approximate depth to which light in the tropics 

 appears to penetrate the sea- water — our task would be com- 

 plicated by an almost complete absence of knowledge of the 

 vertical range of most of the benthos animals ; and in view 

 of its extraordinary range as found by the ' Siboga' Expe- 

 dition it is a factor which could not be neglected by us. 



The subject, however, of our main inquiry would be the 

 extent to which the benthos animals of Bermuda produce 

 definite pelagic larvae and the distances to which these could 

 be carried by the currents. In the course of centuries a few 

 of the animals would doubtless be conveyed over to our bank 

 by means of floating timber or pumice or the feet of birds, 

 much beloved of writers on distribution ; but after full con- 

 sideration we would be inclined to reject these sources as of 

 email account. Our research, in truth, resolves itself into a 



