26 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 128 



to temperature, for example, would become distributed from the 

 Arctic to North Atlantic and North Pacific regions more readily than 

 a species that has a very narrow range of tolerance to the same fac- 

 tor. When the same species of marine animal is found in both the 

 Atlantic and Pacific, it has migrated through the Arctic unless brought 

 around on a ship bottom or sent overland with oyster spat or other 

 transplants. 



The usually accepted premise is that the populations of Arctic 

 marine animals have come from more southern waters. Is this sup- 

 position justified? Time is so vast in its scope that little is known of 

 conditions in the Arctic in ages past. Certainly it has been warmer 

 in the Arctic than now — also colder. Perhaps most Arctic marine 

 species did come from the southward, but it is possible that some 

 North Atlantic species and some North Pacific species came from the 

 Arctic; at least, if they are identical in both these regions they must 

 have migrated through the Arctic Ocean. Distribution of marine in- 

 vertebrates is one phase of the process of evolution, and the collec- 

 tion of data that will support or disprove theories of distribution in 

 the Arctic is essential to determine what part it has played in the 

 establishment of present-day deployment and species. It is hoped that 

 this report will offer some evidence that will assist in arriving at 

 conclusions. 



Within a human generation animals introduced to new coasts have 

 become distributed i,ooo miles or more. For example, within about 

 25 years since it was introduced from Europe, a littorine snail has 

 spread along much of the east coast of the United States. If it de- 

 ployed but 5 feet a year, how long would it take a species to become 

 circumarctic ? The 75th parallel is approximately 1,250 miles long. 

 Since deployment takes place in all directions (in this surmise only 

 two, east and west, are considered), the time required for meeting on 

 the opposite side would be equal to 625 miles times 5,280 feet divided 

 by 5 feet or approximately two-thirds of i million years. There are 

 1,000 million in i billion, or 1,500 times two-thirds of a million — in 

 other words, the required time would be 1,500 times as long as is 

 necessary. 



Practically all marine invertebrates have either swimming larvae 

 or means of locomotion as adults, and for such animals 5 feet a year 

 is far too low an estimate of the rate of distribution. Even those sessile 

 animals without free-swimming larvae certainly can average, over a 

 period of years, more than 5 feet a year. At some stage the larvae 

 become detached from the parent, and as tiny animals they are moved 

 about by the activities of other animals before becoming sessile. In 



