No. 626] SHORTER ARTICLES AND DISCUSSIOX 281 



ter during the last ten years has the sea water been at 0° C. or 

 lower for so long a period as last winter. Beginning with the 

 season of 1908-1909 and proceeding to that of 1917-1918, the 

 number of days for each of the ten winters in which the tempera- 

 ture of the seawater was 0° C, or lower, was 3, 40, 44, 63, 3, 55, 0, 

 65, 36 and 80. Thus 1917-1918 with its 80 days of extremely 

 cold water strikingly outruns any one of the preceding nine 



This winter was conspicuous for the formation of large 

 amounts of anchor frost in the shallow waters about Woods 

 Hole. This frost or ice can be seen forming on the bottom of 

 shallow bodies of salt water when the temperature of that water 

 is at 0° C, or lower. It is apparently due to the freezing of 

 fresh water that, seeping through the land, rises from the sea 

 bottom and solidifies at once on coming in contact with sea- 

 water below its own freezing point. This fresh-water ice is 

 especially destructive to marine animals on the bottom and its 

 great prevalence during the winter of 1917-1918 is probably re- 

 sponsible for the scarcity of sea-urchins and other like forms the 

 following summer. It probably had little or no effect on Sagartia, 

 for this sea-anemone lives chiefly between tides and, therefore, 

 above the level at which anchor frost is found, but as a winter 

 phenomenon this ice is a good index of severity and it is severity 

 in the nature of low temperature that is responsible, I believe, for 

 the almost complete elimination of Sagartia. 



That this sea-anemone was not destroyed by the merely me- 

 chanical effect of ice and waves is seen from the fact that the 

 same stretches on Pine Island that were populated with Sagartia 

 Iiici-CB were, and still are, covered with many specimens of 

 Metridium marginatum. This northern species seems not to 

 have suffered in the least from the severity of the past winter 

 and I, therefore, conclude, since Metridium was as much ex- 

 posed to mechanical injury as Sagartia and still survived m 

 ordinary numbers, that Sagartia succumbed to low temperature 

 rather than to any other factor in its environment. This is in 

 accord with the general belief, originally expressed by Verrill, 

 that Sagartia lucia is a southern species introduced by some 

 accident into northern waters. Granting this conclusion, it is 

 easy to understand why this species has not migrated farther 

 northward into colder waters and why in severe winters it is 

 almost exterminated in localities such as Woods Hole. 



