54 
THE YOUNG SCIENTIST. 
The Development of Frog Spawn. 
TN a recent number of Science Gossip, Mr. 
A. M. McAldowie publishes the follow- 
ing notes on the development of frog 
spawn. A small quantity of this material, 
which will soon be abundant in almost every 
locality, forms a very interesting subject for 
observation under a low power. The fol- 
lowing are the notes referred to : 
* 'About the end of March, 1874 (exact 
"April 8th. Most of the embryos show- 
signs of animation. The movements con- 
sist of alternate flexion and extension of the 
body, the animal folding itself up laterally 
and then straightening itself at intervals of 
about half a minute. Movements first ob- 
served in the afternoon, and continued till 
sunset. 
"Apiil 9th. Movements more active than 
yesterday, but still as restricted as before. 
"April 10th. Movements not quite so 
quick as yesterday, but more extensive and 
fish-like. 
"April 11th. Most of the tadpoles appear 
Fig. 1. Nat. size, March. Fig. 2. Ditto, April 4:th. 
Fig. 3. Ditto, April 8th. Fig. 4. Ditto, April 11th. 
fbog's spawn. 
It will be observed that the figures are in pairs; in each case the left hand figure of a pair shows 
the dorsal aspect, and the right hand figure the lateral aspect. 
date uncertain), I exposed a mass of frog's 
spawn to the light in a glass tank, placing 
it in a window having a westerly aspect. 
There was no fire in the room. The small 
round ovum (Fig. 1) gradually became 
elongated, assuming at first an ovoid form, 
but afterwards one end became attenuated, 
while a small groove formed near the other 
extremity, and on the 4th of April most of 
them presented the appearance shown in 
Fig. 2. As the embryo enlarged, these 
characters became more marked, until, on 
the 8th, the form of the head and the body 
could plainly be detected (Fig. 3). 
to be trying to free themselves from the 
albuminous mass by quick wriggling move- 
ments. External gills very plainly seen on 
all (Fig. 4). They first appeared as two 
small protuberances, situated one on each 
side of the hinder part of the head. These 
gradually elongated, divided and sub- 
divided, until they presented the appearance 
of small branched filaments. 
"April 12th. Tadpoles all out this morn- 
ing. Arrange themselves in clusters with 
their heads all in one direction. Most of 
them remain quite motionless, but a few 
swim actively about the tank." 
