No.49.] | THE ANATOMY OF AXOLOTLS. 895 
glands are swollen and active. The heart and pulmonary 
organs have reached their final form, the former having two 
auricles and a connection with the lungs, and the latter con- 
sisting of the two elongate lungs communicating with the 
throat by means of a glottis. The siredon is thus morpho- 
logically a pulmonate or “air-breathing ” animal, and so it is 
physiologically, for, notwithstanding its aquatic environment 
and branchial equipment, it uses its lungs for breathing. 
A single one of the members of the Colorado series, the one 
numbered 10 in the list, is especially interesting, because it was 
taken in the act of transformation, the process nearly completed. 
The head of this specimen is shown in Figs. 2 4, 3 4, and 5. 
The general appearance of the animal is very similar to the one 
illustrated by Tegetmeier (70). The head is intermediate in 
form between the aquatic and the terrestrial states. Its total 
length is 27% of that of the head and trunk. This is the ratio 
found in land salamanders, while 31-36 is that found in aquatic 
forms. The posterior part of the head, however, is here found 
not to be relatively shortened, as might at first be expected. It 
I$ 72% of that of the whole head, as in siredons, as against 60/, 
the ratio for land forms. As to outline in front, the head is as 
In the land forms, being strongly curved (see Fig. 2 b). The 
skin of the head is tightly drawn and not loose and abundant. 
This tension of the skin produces the bulging of the eyes noted 
by Marsh (68) and Weismann (75) among the changes of the 
transformation, Dorsally the head is arched, as in the land 
forms, and not any longer so flat as in the aquatic stage. The 
mouth opening is not yet as wide as it is in the definitive form. 
The fold at the angle of the jaws has lessened but not entirely 
disappeared, and the angle of the mouth is on the level of the 
“Yes and not behind them (compare Figs. 3 and 3c). Ven- 
‘rally the gular fold has become confluent with the floor of the 
mouth and throat in the center, and some distance from the 
Middle line on each side the vestiges of the gill apparatus 
E^ The three clefts are still present on each side, but 
Er been pushed back and out from the throat, es ah 
. “ed into the small space left behind the gular fold (se 
Ig. 5). Structurally the apparatus is almost completely 
