90 
BULLETIN of the bureau of fisheries. 
increased. After from twenty-four to thirty-six hours all the ripe mussels of a given 
lot were spawned out. It was observed that spawning started soonest among specimens 
which had been roughly handled before being placed in the trough. The duration of 
spawning varied with different individuals. Some would deposit practically all their 
products at one time, which required from twenty minutes to an hour. Others would 
spawn intermittently for short periods of several minutes each and finally stop altogether 
without having discharged half their genital products. 
A male mussel discharges a stream of milt which will color the water for a distance 
of i o or 12 feet before becoming too diffuse to be seen. In quiet water a female mussel 
will discharge her eggs so that they will fall in a heap. They can easily be removed 
by means of a pipette and measured in a graduate, a method which revealed the fact 
that mussels lay from i to 4 cubic centimeters of eggs at a single spawning. Knowing 
the average diameter of the eggs to be 0.07 mm., it is easy to calculate the number in a 
cubic centimeter, which approximates more than 3,000,000. On August 2, 1909, a 
mussel 3X inches long was seen to begin the deposition of eggs. A homeopathic vial 
of about 10 c. c. capacity was immediately placed in such a position as to receive the 
string of spawn as it was discharged. The egg laying proceeded at a remarkably rapid 
rate and continued for 15 minutes, when it suddenly stopped. 
The mussel was watched for an hour longer and, when it was seen that no more 
eggs were to be laid, was removed from the trough and the shells opened to expose the 
mantle. The condition found is shown in figure 4 of plate xix. All of the eggs except 
little patches here and there near the edge of the mantle had been discharged. Of 
course it was not known whether any of the eggs had been laid before this individual 
had come under my observation. The number of eggs laid measured 4 c. c., which 
means that this mussel liberated in round numbers about 12,000,000 eggs in 15 minutes. 
This is possibly more than the number usually produced. Three other mussels under 
my observation liberated from 6,000,000 to 9,000,000 each. 
The period of reproduction varies for different regions and is influenced considerably 
by climatic conditions. It has been hard to determine when the mussel breeds on our 
northern Atlantic coast. Verrill and Smith (1873) and Goode (1887) say that the 
mussel breeds early in the spring. Ganong (1889), writing in Acadia, states that the 
height of the breeding season appears to be April and May. Mr. Charles H. Silverwood, 
of Pawtucket, R. I., who for years has been watching the habits of the mussels in 
Narragansett Bay, writes that the breeding season varies with the weather, beginning 
sometimes as early as the middle of June and lasting until late in August. Mr. George A. 
Carman, of Canarsie, N. Y., observes that the mussels in Long Island Sound spawn 
during April and May, while those in the open ocean do not spawn until about Sep- 
tember 1. My own observations on the development of the sexual organs in mussels 
from Woods Hole, Mass., are in harmony with Silverwood’s statement. Specimens of 
mussels were collected every month from February 7 until August 24. The mantles were 
sectioned and mounted for microscopical examination. The series of preparations 
show a gradual development of the sex cells during the whole period. No mature 
