416 
bulletin of the bureau of fisheries. 
Measurements to determine the rate of growth of Pinna under natural conditions 
revealed slower growth than had been anticipated. In seven weeks’ time some speci- 
mens increased one-half inch in length with corresponding increase in breadth. The 
greater number grew only about one-fourth of an inch in this time and the oldest speci- 
mens showed no growth. It is impossible to estimate from these figures the time required 
for an individual to reach maturity, but the fact is revealed that when they reach a 
certain age growth ceases. 
At the suggestion of Professor Andrews I endeavored to discover whether the 
calcium salts used in shell formation are taken directly from the sea water or whether 
they are taken from the blood. The results are not satisfactory, but I give them for 
what they are worth: A notch was cut in the shell of a young specimen and the broken 
edges were filed until they were quite smooth. The specimen was then placed in artificial 
sea water which lacked only the calcium salts. This water was kept aerated by com- 
pressed air. The specimen applied the mantle edge to the broken place in the shell and 
kept at work for several hours without accomplishing much. During the first experi- 
ment, which was continued for twenty-four hours, only about one-tenth as much shell 
was produced as would have been formed under normal conditions. However, enough 
was produced to be plainly visible and when it was removed and examined under the 
microscope it showed normal structure and effervesced when hydrochloric acid was 
added. 
Several similar experiments were tried, but no perceptible growth of shell was 
obtained. In the first experiment the chemicals used were not “C. P. ” and may have 
had some calcium in them, and this may account for the lack of uniformity in the results. 
It was impossible to keep the specimens in good condition for twenty-four hours in this 
artificial sea water and on this account I think it unwise to draw hard and fast con- 
clusions from the experiments. The method seems worth trying under more favorable 
conditions. Recently the question has been raised as to whether animals which live in 
a water medium can take nourishment from it through the general body surface. It 
seems quite possible that lamellibranchs take the lime salts from the water directly 
rather than indirectly from the digestive tract. If lamellibranchs elaborate shell from 
calcium salts in the blood, their supply must be continually replenished, judging from the 
above experiments, which indicate that these specimens could not make much headway 
from stores already present in the body. 
MANTLE GLAND. 
A large muscular structure, which appears from its connections to have been devel- 
oped from the mantle, lies in the cloacal chamber. It resembles the foot in many respects 
and, like it, can be extended by blood pressure. When extended it becomes slender and 
mav reach a length of nearly 6 inches, but when contracted it is short and thick. Upon 
its tip it bears a large mucous gland. (Fig. 16, M, pi. xlviii.) This peculiar organ is not 
commonly found in lamellibranchs, being confined to the Pinnidae. Many specimens 
were examined in their natural habitat and in the laboratory for the purpose of learning 
