1878. | An Interesting Case of Natural Selection. 615 
AN INTERESTING CASE OF NATURAL SELECTION. 
SAMUEL F. CLARKE. 
N the early part of last spring I obtained a large number of 
the gelatinous egg-masses of one of our native salamanders or 
newts (probably Amédlystoma opacum). They had been deposited 
in a small pond of clear water, in the edge of a wood just out- 
side the city. 
These egg-masses, or bunches of eggs, vary greatly in size, the 
smallest being no larger than an English walnut and containing only 
from five to eight eggs, while the largest bunches are from six to 
eight inches long, more or less oval in shape, and contain from one 
hundred and fifty to two hundred eggs. The bunches are usually 
attached to some water-plant or to an overhanging blade of grass, 
and the gelatinous matter is so translucent that the dark, opaque 
eggs may readily be seen through it. Each egg is surrounded 
by two membranes, between which there is quite a space; and as 
this space, as well as that within the inner membrane, is filled with 
fluid, an admirable arrangement is thus secured for protect- ` 
ing the embryos from any injury to which they might be exposed 
by coming in contact with any hard, unyielding body. 
The eggs were kept in large glass jars and developed quite 
rapidly, the rate of growth seeming to depend upon the purity 
and temperature of the water. After their gills and balancers 
were developed, they emerged from the eggs and began their 
active life in the water. And now I found trouble in keeping them, 
for I was unable to find what they wanted for food. I tried vari- 
ous things but did not succeed in pleasing them. Upon watch- 
ing them closely I soon found that they had developed cannaba- 
listic tendencies and were eating off one another’s gills. _ This led 
me to study their movements still more closely, when I soon dis- 
covered that among the many there were a few, who although 
they came from the same parents and were subjected to the same 
conditions while in the egg, were yet gifted with greater vigor and 
energy than most of their brothers and sisters or cousins. These 
few stronger ones eat off the gills of many of the weaker ones 
and at the same time were enabled to protect their own from mu- _ 
tilation or destruction. 
These favorable conditions, the large supply of food and the © 
_ better aeration of the blood, soon began to show their influence _ 
~ Upon the growth of the individuals thus favored. Within a week 
