JUNE 13, 1884.] 
methods, applied to the propagation of the oyster, 
were not as unpromising as some seemed to suppose. 
This much, at least, was certain, —that a simple 
method of confining the fry so as to prevent its 
escape from partially land-locked waters was practi- 
cable, and would doubtless be found to be a valuable 
aid in oyster-culture in the future. 
Mr. George S. Page read a paper on the success 
with which certain lakes in Maine had been stocked 
with black bass from fish taken from New York. 
A paper was then read by Col. M. McDonald on the 
natural causes influencing the movements of fishes; 
the author remarking, that in aquaculture, as in agri- 
culture, a number of conditions necessarily concur in 
determining production. Many of the conditions are 
capable of being modified by man’s agency. His in- 
fluence in determining increased production, either 
on the land or in the water, is measured by the in- 
crease in average production, which he may effect by 
modifying favorably the natural conditions which are 
under his control. 
The most important condition determining the 
fluctuations in the aggregate number of fish taken 
year by year is the temperature of the medium in 
which they live. In the case of the shad (Alosa sapi- 
dissima), the study of records of water-temperature 
would seem to indicate that it is ever moving, in 
its ordinary migrations, towards a temperature of 60°. 
Assuming this to be true, we should expect in an 
area like the Chesapeake, limited and bounded sea- 
ward by a wall of low temperature, always to find the 
shad in that portion of this area which approximated 
more nearly to 60°. To trace the shad in their mi- 
grations, it is only necessary to determine the shift- 
ing of this area of congenial temperature under the 
influence of the seasons. Our temperature records 
for 1881, 1882, and 1883, indicate, that, for the winter 
months, the area of maximum temperature is not in 
the rivers, nor in the bay, but on the ocean plateau 
outside, extending from the capes of the Chesapeake 
to the Delaware Breakwater. The presumption, 
therefore, is, that the schools of shad belonging both 
to the Chesapeake and the Delaware have their com- 
mon winter quarters on this plateau. When, under 
the influence of the advancing seasons, the waters 
of the Chesapeake and the Delaware bays become 
warmer than those of this plateau, the migration 
into continental waters begins. The proportion of 
the run that will be directed to the Delaware or 
to the Chesapeake will be determined at this early 
period. If the water at the northern end of this 
area warms up more rapidly than at the southern, 
then an undue proportion of the shad will be thrown 
into the Delaware. On the other hand, cold waters 
coming down the Delaware may effect the contrary 
movement, and throw the schools almost entirely into 
the Chesapeake; thus leading to a partial or total 
failure of the shad-fisheries of the Delaware for the 
season. 
When the schools of shad have entered the Chesa- 
peake, their distribution to the rivers will be deter- 
mined in the same way by temperature influences. 
If the season is backward, so as to keep down the 
SCIENCE, 
721 
temperature of the larger rivers which rise in 
the mountains, then the run of shad will be mainly 
into the shorter tributaries of the bay, which have 
their rise in the tide-water belt, and, of course, are 
warmer at this season than the main rivers. Again: 
warm rains at the beginning of the fishing-season, 
and the absence of snow in the mountains, will 
determine the main movement of the shad into the 
larger rivers of the basin; and if, when the schools 
enter the estuaries of these rivers, they encounter 
a temperature considerably higher than that in the 
bay itself, the movement up the river will be tumul- 
tuous, the schools of shad and herring all entering 
and ascending at once, producing a glut in the fisher- 
ies, such as we sometimes have recorded. 
We see, therefore, in the light of these facts, that 
we may have a successful fishing-season on the Dela- 
ware, accompanied by a total or partial failure in the 
Chesapeake area, and vice versa; and, considering 
the Chesapeake area alone, we may have a very suc- 
cessful fishery in the aggregate, yet accompanied by 
partial or total failures in particular streams, under 
the influence of temperature conditions. If statistics 
of the shad-fisheries are to furnish a measure of 
increase or decrease, they must include the aggregate 
catch of the Chesapeake and Delaware River, and, in- 
deed, of rivers much farther to the north. Statistics 
based upon a comparison of the catch in the same 
river, in different seasons, are of no value as serving 
to give a measure of the results of artificial propa- 
gation. 
That the aggregate production of the shad-fisheries 
of the Atlantic coast is on the increase, is shown by 
the fact, that, in the face of an ever-increasing de- 
mand, prices have not only been held at what they 
were in 1879, but have been sensibly reduced. 
Mr. J. A. Ryder made a communication upon some 
of the forces which limit or determine the survival 
of fish embryos, remarking that different species of 
fishes differed very widely in respect to the number 
of ova produced by a single female during one season. 
After a comparison of the habits of the different 
forms, and after some attention had been bestowed 
upon the contrivances intended for the protection of 
the eggs and young which are developed by the parent 
fishes of certain species, as well as the protective 
adaptations developed by different ova, the speaker 
had concluded that the number of survivals out of 
any given brood of eggs was dependent upon the 
amount of such natural protection afforded them; 
that. such a protective influence likewise tended to 
diminish the number of ova produced by a species 
during a single season just in proportion as such 
natural protective agencies were most effectual. This 
view the speaker thought was strongly supported by 
what is known of such species as commit their eggs 
to the mercy of the environment, as in the case of 
cod, with its two to nine millions of eggs left to float 
and hatch on the surface of the ocean; in which case 
a very small percentage of germs ever reach adult 
age, whereas every one of the six to twenty-five eggs 
of a viviparous or nest-building species grows at least 
large enough to begin the struggle for existence with 
