GROWTH AND AGE AT MATUEITY OF THE PACIFIC RAZOR CLAM 
213 
the actual difference was illustrated by the reading on August 5, which was 
Washington, 17.2° C, and Ketchikan, 17° C. 
LARVAL DEVELOPMENT AND GROWTH OF YOUNG 
The spawning season of 1923 presented an excellent opportunity for the study 
of larvse on the Washington coast. Spawning took j^lace in a very short time, and 
the razor clam larva was the predominant form taken in planlrton tows made 
during the time when they were swimming. Three weeks after spawning the 
larval stage appeared in the tows. At that age the shell is transparent and can 
be seen only when shattered by slight pressure. One month after spawning a 
great number of what proved to be half-grown larvae were found in the surf at 
high tide. In tows taken in 4 feet of water at the same time manj' similar larvae 
and some larger ones were found. More were taken at higli tide than at low tide. 
This may have been due to the flood tide raising the larvae out of the surface 
layer of the sand and carrying them in the surf during the remainder of the flood 
and part of the ebb of the tide. As the larvae increased in size more were found 
in the sand, and at the same time the numbers in the tows decreased. All clams 
were considered as larvae until they had opaque shells covered with a brown 
periostracum, and the shape had become markedly elliptical. 
There is no evidence of extensive migration of adult clams. In fact, obsei'va- 
tions point to a very limited range for any individual. The distribution occurs 
mainly during the larval stages. As the period during which the young are in the 
swimming stage amounts to about eight weeks, the excellent set resulting from one 
spawning would indicate that the larvae are largely confined to the sand. If the 
eggs and larvae were free for this length of time they would probably be so widely 
scattered that the original beds would not be heavily stocked. The eggs sink quite 
rapidly and are not easily raised by surf action. They are probably discharged 
at the surface of the sand. If they sink as soon as they have left the body of the 
mother and resist the action of the surf, which would tend to scatter them, they 
would be fertilized in great numbers in the surface layer of the sand. As they also 
spend a large part of their larval life in the sand, it is not surprising that the re- 
sulting set in one place is enormous. HoAvever, the young clams do swim and the 
eggs are doubtless moved about, but apparently not to the extent that might be ex- 
pected from an eight weeks' larval period. 
LENGTH OF LARVAL LIFE AS COMPARED V/ITH OTHER MOLLUSKS 
The length of the larval life of the razor clam seems quite long when compared 
with that of other mollusks. It has been found by Nelson (1921) that the eastern 
oyster {Ostrea elongata) has a free-swimming stage lasting from 14 to 18 days. 
This was determined by direct observation under known conditions of salinity and 
temperature. 
According to Kellogg (1910) the soft clam {Mya arenaria) swims as a larva 
for from three to six daj's. The general observations from which this indetermi- 
nate period was inferred are not very satisfactory. A number of difficulties are en- 
