818 MR EDWARD J. BLES ON THE 
with a gelatinous matrix. It was not possible to make out any circulation of 
lymph or movement of lymph-corpuscles in the tail fin. The first capillaries appear 
near the tip of the tail, and they spread towards the proximal parts, becoming — 
more and more numerous as the time for the resorption of the tail approaches ; 
thus obviously raising the suggestion that the process of resorption is carried on 
by methods connected with this vascularisation. The tail is not used for the respira- 
tory function. 
The limbs now grow rapidly. The arm rotates from the shoulder-joimt through 
90°, and about forty-eight hours after protrusion has left the position shown in fig. 25, 
Plate IV. (where the arm hangs down in a plane at right angles to the long axis of the 
animal) for the adult position: namely, directed forwards towards the mouth and 
lying in a horizontal plane parallel to the long axis. At first the arms are ridiculously 
out of proportion to the size of the head; they have lagged behind in development 
very considerably. The deficiency is made up in three weeks, and by the end of 
the metamorphosis the length of the arms is such as to allow of the fingers just 
meeting in front of the head. The legs are developed in the primitive fin position, 
and, apart from the bending of the limb, are kept in this position throughout life. 
Soon after the stage of fig. 23, Plate IV, where the leg is still in the primitive position, 
the thigh is swung round at the hip-joint until it stands out at right angles to 
the body ; the knee-joint is bent so that the tibia remains parallel to its original position, 
and the ankle is bent so as to turn the foot out through 90°, the sole facing backwards 
instead of inwards. These changes go on during the three days after the arms 
emerge; at the same time the black claws appear on the three preaxial digits, some 
weeks before they come into use. The legs now assist the tail quite efficiently in 
swimming, and grow rapidly, especially the feet. 
The colour of the skin changes gradually in character. Fig. 24 still shows 
the tadpole coloration; two to three weeks later the adult coloration had been 
assumed, and then the whole creature becomes a strange mixture of larva and 
adult. The whole habit is larval; the creature still swims in mid-water in an 
upright position; there is a long tail, mouth and tentacles are unchanged, spiracles 
are present, but the body itself, in shape and colour, and also the appendages, 
are adult in character. In two days after this condition is reached (about fourteen 
days after the arms emerge) the tentacles have almost disappeared, and then the 
mouth very quickly transforms from the larval to the adult state. The whole 
process is finished in four to six hours. When the tentacles are very much 
shrunken, the angle of the mouth, where they were attached until now, seems to grow 
back under them; the gape of the mouth is consequently widened, and at the 
same time the stumps of the tentacles become dorsal to the mouth. A minute 
basal part of the tentacle persists throughout life in Xenopus levis, As the 
mouth metamorphoses the spiracles close up. 
Immediately after the mouth has transformed, the tailed frog ceases to keep 
