44 Mr. J. D. Dana on the Origin of the 



there are warm currents from the south and cold currents from 

 the north. The former overlie the latter to a great extent in the 

 summer, and may aid southern species in northward migrations. 

 Cape Hatteras is nearly the termination of the summer line of 

 70° (see Maury^s Chart), a temperature which belongs to the 

 subtorrid region in winter. On the China coast, at Macao, there 

 is a temperature of SS"^ in July, and in the Yellow Sea, of 78° 

 to 80". But such northward migrations as are thus favoured, are 

 only for the season ; the cold currents of the winter months de- 

 stroy all such adventurers, except the individuals of some hardier 

 species that belong to the seas or have a wide range in distribu- 

 tion. Sea-shore Crustacea are not in themselves migratory, and 

 are thus unlike many species of fish. Even the swimming Por- 

 tunidse are not known voluntarily to change their latitudes with 

 the season. 



The following is a brief recapitulation of the more prominent 

 facts bearing on these points : — 



1. The distribution of individuals of many species through 

 twelve thousand miles in the torrid zone of the Oriental seas. 



2. The very sparing distribution of Oriental species in Occi- 

 dental seas. 



3. The almost total absence of Oriental species from the west 

 coast of America. 



4. The world-wide distribution within certain latitudes of the 

 species we have called cosmopolites. 



5. The occurrence of closely allied genera at the Hawaiian 

 Islands and in the Japan seas. 



6. The occurrence of the same subtorrid species at the Ha- 

 waiian Islands and at Port Natal, South Africa, and not in the 

 torrid zone intermediate, as Kraassia rugulosa and Galene na- 

 talensis. 



7. The occurrence of identical species in the Japan seas and 

 at Port Natal. 



8. The occurrence of the same species {Plagusia tomentosu) 

 in South Africa, New Zealand, and Valparaiso ; and the occur- 

 rence of a second species {Cancer Edivardsii (?) ) at New Zealand 

 and Valparaiso. 



9. The occurrence of closely allied species (as species of Am- 

 j)horoidea and Ozius) in New South Wales and Chili. 



10. The occurrence of the same species in the Japan seas and 

 the Mediterranean, and of several identical genera. 



11. The occurrence of a large number of identical species in 

 the British seas and the INIediterranean ; and also in these seas 

 and about the Canary Islands. 



12. The occurrence of closely allied, if not identical, species 

 (as of Pahxmon) in New Zealand and the British seas ; and also 



