REPORT OF COMMISSIONERS OF INLAND FISHERIES. 
obvious practical value, and the results are given, illustrated by 
numerous photographs, in the reports for 1899 and 1900. The rate 
of growth varies greatly according to the locality, and the varia- 
tion can be referred back still further to two general conditions : 
Ist, the position of the individual clams as regards comfortable 
surroundings ; and 2nd, of more importance, the position in rela- 
tion to the abundance of food-supply. In certain localities, and 
at certain depths of water, the average food-supply is greater than 
at others. Moreover, the longer the water covers the clams, the 
longer time they can feed; for they derive all of their food from 
the water, and can take it only when they are submerged. Other 
conditions being the same, clams grow more slowly near the high- 
water mark. The Japanese take advantage of this fact, as Mr. 
Nishikawa, of the Imperial Fisheries Bureau, of Japan, informs 
me in the following extract from a letter which I take the liberty 
to quote: “In the Gulf of Kojima there is a contrivance to retain 
the shells in their fixed size, for the purpose of export to China. 
The Chinese use only the moderate sized Arca sp., about one inch 
in length. The culturists plant the mollusks densely, at a distance 
from the low-water mark, in beds which are submerged only a 
short portion of the day. By this method the shells can be re- 
tained at the two-years-old size for six or seven years. I am very 
glad to tell you that this contrivance is one which accords with the 
conclusions which you have come to from your own experiments.” 
In some of our experiments, individual clams grew from one-half 
inch to three inches between the middle of July of one year and 
the middle of September of the year following. These three-inch 
clams were about one year and four months old, as they were 
spawned in June. Without taking into account the extreme vari- 
ation, the one-year-old specimens vary between three-quarters of 
an inch and two inches in length. 
Contrary to the opinion ordinarily held, the clams reach sexual 
maturity and breed during the first year of their life. 
In regard to the natural enemies of the clam, it is doubtless im- 
possible to enumerate them all. Of the eggs laid, probably great 
