LIFE-HISTORY OF XHNOPUS LAVIS, DAUD. 8138 
and do so more frequently the warmer the water is, it follows that the lungs are not 
only hydrostatic in function but also respiratory. Reducing the quantity of water has 
the same effect as raising the temperature. It is difficult to follow an individual 
tadpole under normal conditions in a large aquarium, but isolated ones in small 
aquaria will rise every five to ten minutes. 
The tadpole shown in fig. 23 should be glanced at as an intermediate stage 
before proceeding to the typical and final form. This specimen is in the condition 
reached after about two days spent in feeding. During the first few hours feeding 
may be interrupted now and then for a few minutes while the animal suspends 
itself by its cement organ, then this organ begins to atrophy and by this stage 
has completely disappeared. The snout has not yet assumed the characteristic shape, 
which is seen one or two days later. Here it is rounded; but it is important to 
note that there is no trace in this transitional stage of lips like those bearing the 
horny teeth in ordinary tadpoles. W. K. Parker and Brpparp have already drawn 
attention to the total absence of horny teeth. The pronephros and the lymph heart 
are very clearly seen at this stage; the transparency of the tissues is still increasing. 
The contents of the ccelom are, however, beginning to disappear from view, as the 
chromatophores are rapidly increasing in the abdominal wall. The hind limb is. just 
forming as a rudimentary bud. The tail has lengthened and its shape is quite typical. 
A day or two later the appearance of the tadpole has undergone a very obvious 
change. The shape of the snout becomes like that of the advanced tadpole shown 
in fie. 24, Plate IV. It may be described as wedge-shaped, with the lower lip form- 
ine the slightly curved edge of the wedge. The tentacles sprout exactly at the 
angles of the mouth and soon become long slender processes. This stage is one 
which persists for about two and a half months without any marked changes, apart 
from the great increase in size and the growth of the hind limb. It is, therefore, 
the typical larva of Xenopus, but for various reasons I must omit its full description 
here and reserve it for a future communication. The chief reason for so doing is 
inherent in the tadpole itself. It is so transparent in the head region that almost 
all the complicated structure of the vertebrate head can be studied in the living 
animal, and it would be necessary to give accurate figures to make all this clear 
in a description. The difficulty lies in my inability to produce such figures, and, 
as fig. 24 shows, the dead specimen allows very little internal structure to be seen. I 
will confine myself to giving a brief account of the extraordinary feeding habits. The 
tadpoles [ have reared (one male was brought to maturity) were fed exclusively until 
the metamorphosis on pure culture of the green Flagellate Chlamydomonas. They 
thrive best in water which is thick with the Flagellates. In this they float almost 
vertically in mid-water, rapidly undulating the posterior third of the tail and at the 
rate of forty to fifty a minute take in gulps of the water. The water passes out through 
the spiracle ; the Chlamydomonas are retained by the filters in the buccal cavity and 
drawn into a ciliated groove on either side of the pharynx. In this groove the green mass 
TRANS. ROY. SOC. EDIN., VOL. XLI. PART III. (NO. 31). 119 
