Presidential Address. 281 



and my own collections prove that many of the shallow- 

 water forms are common. Dall and Whiteaves 1 have 

 shown that some mollusks and Echinoderms are common 

 even to the Atlantic and Pacific coasts of .North America ; 

 a remarkable fact, testifying at once to the fixity of these 

 species and to the manner in which they have been able to 

 take advantage of geographical changes. Some of the spe- 

 cies of whelks common to the Gulf of St. Lawrence and the 

 Pacific are animals which have no special locomotive pow- 

 ers even when young, but they are northern forms not pro- 

 ceeding far south, so that they may have passed through 

 the Arctic seas. In this connection it is well to remark 

 that many species of animals have powers of locomotion in 

 youth which they lose when adult, and that others may 

 have special means of transit. I once found at Gaspe" a 

 specimen of the Pacific species of Coronula, or whale- 

 barnacle, the C. regince of Darwin, attached to a whale 

 taken in the Gulf of St. Lawrence, and which had probably 

 succeeded in making that passage around the north of 

 America which so many navigators have essayed in vain. 



But it is to be remarked that while many plants and 

 marine invertebrates are common to the two sides of 1he 

 Atlantic, it is different with land animals, and especially 

 vertebrates. I do not know that any palaeozoic insects or 

 land snails or millipedes of Europe and America are specifi- 

 cally identical, and of the numerous species of batrachians 

 of the Carboniferous and reptiles of the Mesozoic all seem 

 to be distinct on the two sides. The same appears to be 

 the case with the Tertiary mammals, until in the later 

 stages of that great period we find such genera as the horse 

 the camel, and the elephant appearing on the two sides of 

 the Atlantic ; but even then the species seem different, 

 except in the case of a few northern forms. 



Some of the longer-lived mollusks of the Atlantic furnish 

 suggestions which remarkably illustrate the biological 

 aspect of these questions. Our familiar friend the oyster is 

 one of these. The first known oysters appear in the Car- 



1 Dall, Report on Alaska ; Whiteaves, Trans. R. S. C. 

 19 



