160 THE MICROSCOPICAL NEWS, 
of developing its muscular power, and of throwing or getting rid 
of the black pigment matter which covers the young tadpole, and 
renders it very opaque. When this is thrown off it assumes a 
brownish grey colour, when the capillary circulation may be seen 
in the tail. From its emerging from the egg the circulation may 
be observed in the gills; when the young tadpole emerges from 
the egg its system is quite elementary. The head, being unusually 
large in proportion to the body, is split or opened a little on the 
under surface, by means of which the young tadpole is able to 
attach itself to any surrounding object. In this state it remains, as 
I have said, for about two days, seemingly without either eyes, 
ears, or mouth. On the sixteenth day 2 somewhat sudden change 
takes place. The mouth has separated with a pair of ‘soft pro- 
truding lips, while the eyes and ears are quite visible. A groove 
also separates the head from the body. The tail has also expanded, 
and become partly transparent, and the lips assume a horny 
appearance. 
The little animal has now developed into a perfect tadpole, and 
with the completion of those changes begins the interesting 
microscopic observation of the circulation of the blood, and the 
development of its internal organs. In studying the habits and 
development of aquatic animals the first principle to be mastered, 
if our experiments are to be of value and carried to a successful 
issue, is that we must be able to set up an aquarium on scientific 
or natural principles, so that the water shall remain sweet and pure 
for any length of time without change, by being thoroughly 
balanced with vegetable and animal life. In this we recognise 
the great fact that vegetable and animal life are co-existent, and 
that the one cannot exist without the other for any length of time. 
It is rather a remarkable fact that it is only about forty-four years since 
the first attempt was made to do this successfully by naturalists, 
and to study the habits of marine animals at home, Dr. N. B. 
Ward having solved the problem introduced by Sir John Dalyell 
in 1790, who employed men to bring up fresh supplies of sea 
water daily, and change the water once and twice a day in his 
tanks and jars. In this manner he spent largely of time and 
money in hopeless and ruinous failures by shutting his eyes to the 
simple means employed by nature in every way-side pond, where 
we find it furnished with an ample supply of aquatic plants. But 
as failures are often the stepping stones to success, so it was in this 
case. I am sorry to say, however, that erroneous notions still 
continue. It iscommon to hear or to see it written, “‘ Change the 
water occasionally.” Now the water in our ponds are not changed 
further than by evaporation, and an occasional drop of rain or surface 
water. So the water in my experiments was not changed from 
beginning to end, but to make up for evaporation a little water was 
