176 THE MICROSCOPICAL NEWS. 
individual animal need to be treated or examined more than once 
when the external gills are fully extended ; put one on water diet, 
and each week must see another subjected to the same treatment. 
When the first is ready for examination note down its form and 
characteristics ; in about a week note the development of No. 2 
during that period; in another week No. 3 will come under 
observation ; and so you will proceed until the frog is reached, 
having at all the intermediate stations noted its progress. ‘That 
those scientific examinations may be successful sunshine and 
attention are indispensably necessary. Carelessness will certainly 
mar the results. This is a case in which the water must be 
changed every day, as there are no plafits to absorb the carbonic 
acid, and give out oxygen. But before the tadpoles aré put into 
the fresh water it must be of the same temperature as the old. If 
this is not done the animals suffer in health. Perhaps the easiest way 
of making both alike in temperture is to let the fresh stand in the 
same room for an hour or two. Then at intervals of three or four 
days I give them a treat by putting them into water rich in 
animalcules for two hours. This change of the water, then, at 
equal temperature, with plenty of light, and keeping the water 
clean, is the secret of success. A fortnight of this treatment, 
simply a process of starving to reduce the number of red corpuscles 
in the blood from the want of food, causes the intestines also to 
get empty, and partly transparent, the kidneys, heart, and lungs also 
partake of this partial transparency. In this state, if put into a 
white basin or saucer with a beam of sunlight, we shall see with 
the naked eye the top side of the heart oscillating ; the intestines 
opening and contracting ; the lungs heaving, the eyes rolling, and 
the mouth working. While in the shadow will be seen the 
duplicate of these movements from the under side. If they are 
now transferred to the zoophyte trough the sight will amply repay 
any trouble a thousand times over. 
If at about 30 days old from the deposit of the egg you examine 
with a magnifying power of about 20 or 25 diameters, with the 
upper part of the tail and the lower part of the body in view, we 
see the blood in the main arteries flowing outwards to the tail, 
while other streams of equal volume flow inwards through the 
veins. Just at the lower part of the body may be seen two brown 
projections forming an obtuse angle. These are the kidneys, 
where the blood may be seen flowing in at one side and out at 
the other. Then, by moving the stage, leaving only the top of 
the kidneys in view, we have a sight which is not to be surpassed 
in the whole realm of nature, viz., the kidneys at work, the heart 
oscillating, the intestines expanding and contracting, the gills 
waving. We see in this view the four principal organs of the body 
harmoniously devoted to the getting rid of waste matter, and the 
