BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 177 
number of species belonging to this category (though not these in particular) do repro- 
duce sexually during the summer months. In few cases, if any, however, do we know 
from local observations that their sexual period is confined to these months. We may 
comment parenthetically upon the urgent need of determining the reproductive condi- 
tion of local marine organisms throughout the entire year. 
In the case of one species among those which appear to be restricted to the warmer 
waters of the region we have definite evidence that an actual destruction of adult organ- 
isms may occur as a result of extreme cold in winter. We refer to the common sea urchin, 
Arbacia punctulata, which, as our records show (see pp. 114, 115), was almost exterminated 
in Vineyard Sound during the winter of 1903-4. And it is well known to fishermen and 
others that great numbers of dead fishes and mollusks of certain species are frequently 
found after a particularly hard spell of cold weather.? This is sometimes attributed 
to the action of “anchor ice”’ or “ground frost.”? Gould (1840) cites the case of an 
extensive destruction of oysters which was believed to be due to this agency. That 
anchor ice does form in salt water, even at the depth of a number of fathoms, and that 
it may “freeze around fish caught in nets,”’ is vouched for by Sir William Dawson and 
others.° On the other hand, we are informed by Prof. Herdman that he has had personal 
knowledge of the death from cold of fishes in aquaria, and even of burrowing mollusks 
along shore, in cases where actual freezing was out of question. It seems difficult, indeed, 
to believe in such a wholesale formation of anchor ice throughout Vineyard Sound as 
would be necessary to account for the extermination of the sea urchins by this agency. 
However, the extermination did occur during an exceptionally cold winter, and it seems 
a legitimate inference that it resulted in some way from the cold. 
Now it is known that Arbacia finds in this region its northern limit of distribution 
upon our coast. It would seem, therefore, that in this latitude it is adapted to withstand- 
ing the average winter but not the exceptional one. On the other hand, no mere refer- 
ence to.winter temperatures can explain the absence of this species from the western end 
of Vineyard Sound, or from Crab Ledge. For, although at these latter points the sum- 
mer temperatures are considerably lower than they are nearer Woods Hole, the winter 
temperatures are no lower, and possibly, indeed, not solow. Here, then, the law of Mer- 
riam may have application. Arbacia may not be adapted to reproducing in these colder 
waters. 
But Merriam’s principle, in its completed form, really contains two wholly distinct 
principles. The second is that animals are “restricted in southward distribution by the 
mean temperature of a brief period covering the hottest part of the year’’ (1895, p. 234). 
It is not stated whether this effect has to do with the ability of the adult organism itself 
to withstand higher temperatures, or whether the reproductive power is curtailed. 
As regards the distribution of our local marine fauna, this phase of Merriam’s law 
can apply, if at all, only to those predominantly northern species which were found to be 
restricted to the waters which were cooler during the summer months. And it does seem 
likely, indeed, that some of these species are unable to endure the high temperatures 
@ Aside from the case of certain fishes, our data for the winter months are derived almost wholly from an examination of 
tow-net collections made by Mr. Edwards. 
> The scraping action of ordinary floating ice in removing the rock-weeds (Fucus and Ascophyllum) from the boulders along 
shore is pointed out in the botanical section of this report. ‘This same agency doubtless restricts the distribution of such littoral 
animals as inhabit these weeds, and may even affect certain other forms, e. g., barnacles, which occur directly on the rocks. But 
it can, of course, have no influence upon the benthos, with which we are especially concerned here. 
¢ Cf. Barnes, 1906, p. 210, 223-225. 
16269°—Bull. 31, pt 1—13 
I2 
