THE DEVELOPMENT OF THE FROG. 175 
effect a full development ; pond water being used with the first of 
his specimens, the number of which was not given, and it is quite 
possible that eight days might separate the first from the last, being 
only one day under the average of four years in my experiments. 
I now propose, for the benefit of young members, or those who 
have not had any experience with tadpoles, to say a few words 
on the process usually called putting the tadpoles on water diet, as 
the majority of books give nothing but the mere statement with 
no details. This defective book-lore, to my certain knowledge, 
leads in some cases to cruel and barbarous treatment of the tadpoles 
until friendly death releases them from their torture ; whereas, if pro- 
perly treated, the animals experience no bad results. I have put 
some hundreds through this ordeal, and I do not remember losing 
one by it. In my experience the tadpole is a hardy animal, which 
may be reared as successfully in confinement as in its native pond 
in the open air. I may further add that I have satisfied myself as 
to the injurious effects or otherwise of this water treatment. I find 
the tadpoles exhibit more spirit after this than those who have not 
been subjected to it, although the time of their ultimate develop- 
ment is lengthened by one half; that is to say, if the treatment 
has been continued for say 14 or 20 days, the time needed for 
their full development will be extended by 7 or ro days respec- 
tively. In no case should this treatment exceed 20 days, as 
about this time they begin to show signs of suffering, and assume 
a sickly appearance, and in a few days usually die. My usual time 
is 10 or 14 days; if I cannot get them to what I want in that 
time I have to be satisfied. Still, the best results will be obtained 
when the weather is bright and clear, as under the absorbent 
power of light the black pigment cells in the skin soon yield to its 
influence, and quickly disappear altogether. I have often observed 
these pigment cells elongate until two of them united, then the 
contents of the one would run into the other, indicating, in my 
opinion, one of two things: either under the influence of light this 
pigment matter dissolves or liquefies so as to be easily absorbed 
and assimilated as food, or else escapes outwards through the skin. 
Most observers rest content by seeing the capillary circulation in 
the tail. This, no doubt, is in itself a grand sight, and there may 
be some who imagine that more than this is impossible, and that 
what I have said to-night about seeing their internal organs at 
work, so as to recognise their change and development, and be 
able to follow the arterial and venereal flow of blood through 
every part of the body, is but an idle dream or a fond fancy. If 
there are any such sceptics I most respectfully ask them to carry 
out for themselves the following simple details, when they will 
receive ocular proof of the truth of my assertion. 
‘In the first place obtain, say, a dozen tadpoles, so that no 
