THE YOUNG 
SCIENTIST. 
<cles, nerves, bones, and blood-vessels 
atrophy, and vanish from our sight. 
They have not faded away ; they have not 
simply fallen off ; they have not been cast 
off by a species of moulting, as in the case 
of insect larvae. They have been got rid of 
by none of these methods ; their substance 
has been reabsorbed, atom by atom, and 
hence, although it has ceased to exist, it 
is not the less alive on that account. 
We see, then, that frogs undergo com- 
plete metamorphosis, not only in regard 
to their entire organism, but as to each 
set of apparatus, with the exception of the 
nervous system." 
Frogs generally spawn about the middle 
of April, at which time they become very 
musical. 
The ova or eggs of frogs consist of small 
round opaque bodies, enclosed in a jelly- 
like substance. This jelly-like substance 
is for the purpose of protecting the egg 
from its natural enemies as well as to 
afford support during incubation. The 
egg or embryo, consisting of a small glob- 
ular body, darker on one side than the 
other, begins to show development within 
twenty-four hours, the black globes 
lengthen out, and in forty-eight hours 
the head and tail are well defined; the 
fm around the tail now appears, and from 
each side of the neck the lungs or 
branchiae begin to start. In about two 
weeks' time after the eggs were depos- 
ited, the "tads " having absorbed a large 
portion of the jelly-like coating, break 
through, and become free. Their lungs 
now attain their full development, but in 
course of time disappear, being drawn 
into a cavity, where they are covered by a 
fold of the skin resembling the gill cover 
of a fish. The tadpole now grows very 
rapidly, feeding constantly on confervas 
and decaying vegetable matter. 
In the course of a few weeks small pro- 
jections begin to appear towards the fore 
and back part of the body ; these are the 
legs just beginning to develope, and, as 
they grow larger each day, the "tad" be- 
gins to learn the use of them, frequenting 
very shallow water, and rising constantly 
to the surface to breathe, for by this time 
the gill covers have closed up, and in place 
of them he now has perfect lungs and 
breathes free air through his nostrils. He 
is still in full possession of his broad 
fleshy tail, which seems to be greatly in 
his way, and is all that is left to remind 
one of his former tadpole condition ; but 
in course of time this is gradually ab- 
sorbed, till nothing is left of it but just 
the tip end. He now seeks the shore, and 
becomes carnivorous. 
The tadpole having become a frog is 
"small but pleasing to the eye," and is 
an excellent subject for an aquarium. 
Frogs raised in an aquarium are always 
to be preferred, as they are more domesti- 
cated, will feed from the hand, and are less 
liable to wander away. When domes- 
ticated, they are very partial to "croton 
bugs" and roaches, but will not take 
dead food, though I once had a very large 
frog which fed on raw beef, but the pieces 
of beef had to be kept in motion so as to 
cause him to think they were possessed of 
life. 
Iron Floating on Water. 
WE have all heard of the wonderful 
miracle, by which the Prophet Elisha 
caused the iron head of an axe to float on 
the water of the river Jordan. And the 
floating of iron ships is something with 
which we are all familiar, either from 
having heard of it, or from having seen it. 
A tin or iron cup or basin will readily 
float, provided it displaces an amount of 
water greater in weight than the weight 
of the metal in the vessel. But even a 
solid rod of iron may be made to float 
provided it is small enough. Take a fine 
needle, wipe it with an oily rag, but do 
not leave any visible trace of oil on it, and 
then lay it gently on the surface of water 
in a basin ; it will float, and continue to 
float for some little time. The cause of 
this is the fact that a quantity of air ad- 
heres to the needle sufficient to buoy it 
up. Moreover, as the cohesion between 
the particles of water is considerable, and 
as water has no attraction for a perfectly 
dry piece of steel, the cohesion of the 
water is greater than the weight of the 
metal; and so the latter is supported. 
In the same way insects are enabled to 
' walk upon the water. The hairs on the 
