812 MR EDWARD J. BLES ON THE 
raised rim incomplete behind. The median swelling behind the olfactory pits is 
caused by the brain. The eyes stand out prominently from the side of the head. 
In the side view there are very obvious alterations to be observed in the proportions . 
of the parts of the animal. At hatching the tail was only one-third of the total length ; 
it is now two-thirds, while the abdomen, which was very elongated, now appears very 
short in proportion. The fin-fold has grown considerably, and has grown out from 
below the abdomen, drawing out the cloaca, so that the cloacal opening comes to lie at 
the edge of the fold. The pronephros tubules can be seen quite distinctly through the 
transparent skin. 
The Lymph Hearts.—Just behind the pronephros on each side is the newly de- 
veloped lymph heart. It lies in a small lymph space immediately below the skin on a 
level with the inner ccelomic outline of the pronephros. It can be best located in the 
living animal by the movements of the nearest chromatophore of the skin, which, under 
the microscope, are more conspicuous than the pulsations of the lymph heart itself. 
Delicate trabeculze run across the enveloping lymph space from the heart to the integu- 
ment, and these pull down the skin at each contraction of the heart. At this stage the 
pulsations are very irregular; they sometimes cease for one or two minutes, and seldom 
continue uninterruptedly for even twenty beats, hence it is dithcult to time them. 
When most regular they average forty beats a minute. 
This early appearance of the pectoral lymph hearts is after all not very remarkable 
when the extent and physiological importance of the lymph spaces in the tadpole is 
considered. However, the find was an unexpected one, as I had already paid a little 
attention to the subject and found that the pelvic lymph hearts do not appear in &. 
temporaria and Bufo calamita before the metamorphosis. 
The Tadpole.—tIt is not ditticult to notice the commencement of feeding in a batch of 
young tadpoles. Those which have not begun, only swim about fitfully and then hang 
by the cement organ, the breathing movements continuing while they hang. Those which 
have begun to feed are suspended in mid-water, making little or no progress, and are 
steadily gulping away ; the feeces appear in the cloaca within twenty minutes or half an 
hour afterwards ; thus the time at which the alimentary canal is open to the passage of 
food can be easily and definitely fixed. This is important, because it makes the follow- 
ing interesting fact easy to determine by watching at the correct time, namely, that 
within two hours after beginning to feed the tadpoles rise to the surface for air and 
begin to use their lungs as breathing organs. Brpparp observed that Xenopus does not 
develop “internal” gills (94, p. 106) and concluded that respiration was carried on 
through the blood-vessels of the “filters” placed on the internal side of the branchial 
arches. His observations are correct, but as he paid no attention to the use of the lungs, 
he was led to a conclusion which turns out to be of subsidiary importance. It is 
possible that a certain small amount of oxygenation of the blood does go on in the pro- 
cesses of the filtering apparatus. And until feeding commences respiration is carried on 
by the external gills. But as the tadpoles are constantly rising to the surface for air 
