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mass, and no commencement of the organs which it after- 
wards contains is yet made. Two other organs, however, 
have been formed, the use of which is temporary, and 
confined to the second period ; these are the sucker and the 
external gills, and they are already so far developed as to 
be perfectly efficient when the tadpole escapes. The sucker 
is at first large and single, extending across the middle line, 
and it is in this condition when the animal is hatched. The 
external gills, two on each side, have attained such a size as 
to serve at once as organs of respiration. 
The second period extends from the time of hatching to 
the completion of the mouth and alimentary canal, and the 
commencement of feeding ; it, like the first period, occupies 
about a fortnight. The special temporary organs now in 
use are the sucker, which soon divides into two, and the 
external gills. The developments which take place are 
those of the bronchial arches and clefts ; the internal gills ; 
the eyes; the gill-chambers, formed by the opercular fold, 
which begins to grow on the second day and is completed 
on the fourteenth; the passages of the nostrils to the back 
of the mouth, these being in connection with the internal 
gills, the ciliary action of which draws water through them ; 
and the suctorial, beaked mouth and coiled alimentary canal, 
peculiar to the tadpole. 
This second period is a continuation of the embryonic 
condition ; contact with water and aquatic respiration are 
necessary for further development, but rest is also required, 
and the animal continues as stationary as whilst in the egg. It 
is blind and helpless, and cannot feed, having no alimentary 
canal. Immediately on its escape the tail is used, but only 
to swim to some fixed object to wiiich it attaches itself by 
its sucker, and there it remains till the close of the period, 
unless forcibly detached, when it at once refixes itself. 
The suckers, though efficient almost to the end of the 
period, daily diminish in size and have disappeared at its 
