LIFE-HISTORY OF XENOPUS LA:VIS, DAUD. 819 
constantly to its larval free-swimming habits, and spends more and more time 
lying on the bottom. At this time the tail has begun to atrophy, the blood- 
vessels in the fin spread, the notochord at the tip becomes wavy, and the pigmenta- 
tion darkens. At the end of a week the greater part of the tail is absorbed; 
about one-third of it is left, very deeply pigmented, and the young frog has thus 
reached the stage at which the typical Phaneroglossan lands and becomes terrestrial. 
There is not the slightest tendency to land in the case of Xenopus. It swims 
about actively in search of food, and for some weeks lives on small, free-swimming 
Crustacea. Seven specimens reared to this stage consumed enormous quantities 
of Daphma pulex; a great swarm of these vanished every twenty-four hours, and 
the frogs throve. 
Their hands are at once used in the grown-up manner to cram the food into 
their mouths; the arms are not used for progression at all, except to push aside 
water-weeds—hence one of their functions as limbs has almost disappeared. The 
size of the arm is altogether out of proportion to the size of the leg, which is an 
extremely powerful swimming organ. The limbs of Xenopus as a frog are paralleled 
by the limbs of Macropus as a marsupial. 
When W. K. Parker (76) described the skull in larval Xenopus, he laid 
stress upon what he considered Chimeroid features in the chondrocranium, and 
was naturally led to attach morphological importance to the lash-like tail end of 
the Xenopus tadpole. Now, although this close resemblance does not exist, there 
is a certain degree of resemblance which suggests similarity of function. The end 
of the tail of the Xenopus tadpole has a very narrow dorsal and ventral fin-fold 
(see figs. 23 and 24, Plate IV), and it is easy to see in the living animal that 
the constant undulatory movement of this narrow membrane has very little 
propelling power. The suggestion is, then, that the Xenopus tadpole, Chimera, 
and such fishes with a narrow lash-lke tail end as the Mormyride, use that part 
for suspending themselves either in mid-water or, in the case of bottom - feeders 
or mud-feeders, just over the bottom, by means of a rapid undulatory movement. 
Sexual maturity appears to be reached at an early age. One male was kept 
until two years old, when it began to pair. 
