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feed voraciously, and grow very rapidly. During this period 
water continues to he taken in through the nostrils to supply 
the gills, and the opening by which it is discharged from the 
gill-chamber becomes tubular, extending upwards and back- 
wards, embedded in the skin until it terminates in a short 
conical tube projecting from about the middle of the left 
side of the body. The mouth consists of a pair of strong, 
brown, homy beaks, with serrated edges, and is surrounded 
by a broad expanded sheet of white fleshy membrane, 
irregularly frilled and scolloped at its edges. Its inner or 
front surface is furnished with long rows of small brown 
teeth set upon white, apparently cartilaginous bands, so 
that they resemble combs. There are three sets of these 
combs on the upper and four on the lower lip. The 
alimentary canal in the abdomen consists of a long simple 
tube of equal diameter throughout, and about three and a 
half times the length of the tadpole ; it is folded in half, and 
thus doubled, is coiled round and round, filling the left half 
of the abdominal cavity, and forming in its final coils the 
regular flat spiral seen on removing the skin of the ventral 
surface. 
The fourth period extends from the fiftieth to the seventy- 
fourth day. Feeding is very active, and rapid growth 
continues. The developments which take place in it are 
those of the limbs, with the shoulder girdle and pelvis, and 
the lungs. Water no longer enters by the nostrils, but 
passes through the mouth. The pair of papillae, seen on each 
side at the root of the tail as early as the thirtieth day, now 
begin to enlarge at their ends, become broader, and at length 
divisions marking the toes appear, at the same time the knee 
and ankle are indicated by bendings in the lengthening 
limbs. In fifteen days both fore and hind legs may be said 
to be fully formed, though the toes of the hind pair are still 
without webs. The development of the fore legs within 
the gill-chamber advances equally with the hind legs. At 
