life, concurrent with, the passage of time, is evident, especially to geologists ; but of the way in which these changes have been carried out, I own to not yet seeing a sufficient explanation. Have terraqueous changes led to variations in the structure of animal life by the law of Natural Selection among the few that best adapted themselves to the changed conditions ? or was it by a gradual modification induced in the many, in consequence of the general change to which they were all subjected ? or was there some law in time, or of a character yet unknown to us, cooperating with the change in conditions, to produce those singular and extraordinary changes and variations of structure of which we have now such full evidence as to fact, but so little as to theory ?
These are some of the problems towards the solution of which I look with great hope in the continuance of these most interesting deep-sea researches, important alike to the naturalist, the physicist, and the geologist.
P.S. The few particulars in this Address relating to deep-sea temperatures were collected some twenty years since for a paper never published. As they form fitting antecedents to the more important recent researches, I have incorporated part of them here, leaving possibly some of the intermediate work rather incomplete.
Note. — Since the greater part of this Address was printed, Mr. Jeffreys informs me that he has now, through the kindness of Prof. Loven, examined the shells procured in the Swedish expedition of 1869 by dredging on the Josephine Bank and off the Azores, at depths ranging from 110 to 790 fathoms ; and that nearly all these shells belong to the same species as those procured in the ' Porcupine ' expeditions at similar depths.
