FOOD VAL,UE OF SEA MUSSEES. 
91 
sexual products were observed before July 3. On that date I found spermatozoa, 
which, when placed in sea water, were very active; they clustered about the eggs and 
by their active movements caused the eggs to slide gradually hither and thither across 
the microscopic field. 
In England, on the Lancashire coast, Scott (1901) found that the mussels do not 
breed until midsummer. He kept the mussels in tanks under constant observation 
for a year and made frequent comparisons with those in natural beds. The sex organs 
developed at about the same rate in the two lots. The first eggs were discharged on 
May 6 by individuals in both the tanks and the beds. No spermatozoa, however, were 
observed until June 13 and the first developing eggs were found on June 14. The spawn- 
ing season continued up to the middle of July. In France, where the water is much 
warmer than on our coast, the mussel spat appears in February and March. It is clear 
from the above evidence that the mussel breeds at various times between the months 
of February and September according to the temperature of the water in which it lives. 
The ripe egg is a spherical body so small as to be hardly visible to the naked eye. 
It is surrounded by distinct membrane. On account of the great number of opaque 
yolk granules which fill the egg, none of its internal structures, such as the nucleus 
and nucleolus, are clearly visible under the microscope. The spermatozoa are pin shaped, 
with a conical protuberance upon the head. When liberated in the water they swimabout 
actively and show great tenacity of life. Specimens placed in a bowl of sea water kept 
up active movements for more than six hours. 
It has been an open question whether fertilization of the eggs takes place within the 
body of the female or not. M’lntosh (1885) and Wilson (1886) believe that it is accom- 
plished outside of the female. That this is possibly so, Wilson has demonstrated by mix- 
ing ripe ova and spermatozoa in a beaker of sea water. He obtained the sexual products 
by mincing up portions of the mantle of the two sexes. Scott (1901), who studied the 
mussels kept in tanks, believes, on the other hand, that fertilization of the eggs takes place 
in the branchial chamber of the mother. He observed that “the embryos flow from the 
female in a slow, distinct stream.” If the water is quiet, they settle on the bottom, 
forming a pinkish mass. In this position they continue to develop for from eight to 
twelve hours, finally becoming ciliated larvae, which rise to the surface and swim about. 
At this time they are borne hither and thither by the tidal currents for about four days, 
so that eventually they reach almost every yard of our coast line within their range. At 
the end of this period the larvae undergo important changes. They develop a shell and 
settle upon seaweeds, hydroids, or other convenient objects for attachment. At this stage 
they vary from tJt to of an inch in diameter. The foot now becomes the chief organ 
of locomotion. By means of it they can creep from unfavorable situations over seaweeds 
and other objects to a more suitable position. In young forms the foot is capable of 
great extension and has the appearance of a long, white, flexible thread. By extending, 
attaching, and contracting this foot, the mussel readily draws itself forward. Of the 
myriads of brood mussels that appear shortly after the breeding season, only a small 
portion ever reach suitable places for growth, and of these only a few are destined to 
reach maturity. 
