418 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [24] 
During our stay of ten days the run of mackerel was small; and the 
catch for this reason was very limited; but enough were taken to give 
an opportunity for settling most of the questions that presented them- 
selves, and to furnish an abundance of eggs for the experiments. A 
visit to the pounds proved that the relative number of males and 
females in a school varied considerably. At times the males were 
taken in greater numbers, while again the females were more abundant. 
It was further found that a large percentage of the fish taken were still 
green, though ripe males were not uncommon, and half a dozen or more 
were seen at every lift of the pound. Ripe females were less plenty, 
though many containing a few clear eggs, which were usually too im- 
mature for hatching purposes, were captured. 
On our first visit to the pound-nets one ripe female was found, from 
which about 50,000 eggs were taken and successfully impregnated. 
The manner of “stripping” the mackerel was similar to that employed 
with the shad and other species, the fish being held firmly with the left 
hand, while with the right the eggs were gently pressed from the abdo- 
men into a large pan partially filled with water, where they were easily 
impregnated by being brought in contact with the milt of the males. 
The eggs of the mackerel, and indeed of all other fishes thus far exam- 
ined, are covered by an outer shell or membrane which surrounds and 
protects the germinal mass. When first excluded from the female the 
egg is soft and shapeless, owing to the looseness of this covering mem- 
brane, which is always more or less wrinkled or folded. It has but 
one opening in its surface, this being a small porous disk called the 
micropyle, through which the spermatozoa find their way to the germ 
cells. When placed in water in which the milt has been introduced, 
an absorption of water begins, and soon the membrane becomes 
somewhat disteuded and finally expands to its fullest extent, being 
separated from the germinal mass by a cushion or layer of water, 
which serves to protect the embryo in its earlier stages of develop- 
ment, and in addition furnishes oxygen to sustain the life of the fetus. 
When fully distended by the water the egg is much larger than at the 
time of its exclusion from the parent, the relative increase varying 
with the species from one-fifth to over half of the entire bulk. ‘he 
egg-membrane becomes toughened during the process, and within half 
an hour after impregnation has assumed a globular form and is so 
strong that it can with difficulty be broken by pressure between the 
thumb and finger. This increase in the size of the eggs, due to the ab- 
sorption of water, is, as has been said, very marked in many species, and 
a quantity of eggs that before impregnation scarcely more than half fill 
a dish, will, when fully expanded, ofiert more than fill the vessel so that 
some will be forced over the top. When eggs have thus increased in 
bulk they are said by the spawn-takers to have “ come up,” and the vessel 
containing the milt should then be replaced by clean water, after which 
they are ready for the hatchery. <A slight absorption of water often, 
