8 AViiiTNEY; on the Cimdation in the Tud^wle. 
penter (and as we have also observed) is devoted to the head ; 
but Dr. Carpenter does not mention any connexion between this 
vessel and the lung. Now, this cephalic artery, as it travels 
over and rests upon the upper surface of the lung, receives 
into it smatl branches from the subdivisions of the putmonary 
artery, so that there is a direct communication between these two ^ 
vessels. The second and third trunks, according to the same 
authority, form the aorta, the current flowing continuously 
from the heart into the abdomen ; while a fourth trunk is 
mentioned by Dr. Carpenter as the pulmonary artery, devoted 
exclusively to the lungs. But our own observations have 
convinced us that it is the second trunk which enters and is 
distributed through the lung as the true pulmonary artery, 
while the third trunk also enters and passes through the lung, 
inosculating, in its course, with branches of the pulmonary 
artery, and then emerges from the floor of the lung to enter 
the abdomen, and with its fellow form the aorta or great 
systemic trunk. With regard to the fourth vessel, which Dr. 
Carpenter calls the 2^ulmonary, we have never been able to 
discover such a one. Now, according to Dr. Carpenter's 
view, it is clear that the blood in the cephalic arteries, and 
the blood descending to the aortic trunk in the abdomen, is 
the mixed arterial and venous blood expelled from the heart, 
in short, the blood of a reptile. But the habitudes of the 
tadpole are not those of the reptile. He exhibits all the 
activity and liveliness of the fish long after the gills (the 
characteristics of his fish life) are supplanted by the developing 
lungs. Activity characterises every function in the tadpole 
at this period. In this respect he presents a contrast to the 
frog, which cannot fail to strike the most careless observer. 
The functions of nutrition, growth, development, and 
locomotion, which constitute the great business of his 
life, are all habitually and vigorously performing. For 
these functions, and for this activity, a constant supply of 
pure, aerated blood is known to be essential. On the other 
hand the circulation of mixed venous and arterial blood in 
the frog is consistent with the lethargy, inertness, coldness, 
low vitality of the creature. Dr. Carpenter observes, the 
correspondence between the general vital energy in any in- 
dividual system, and the activity of respiration, must be 
evident to the observer and quotes for example the 
energy of respiration in the active and rapacious eagle as 
compared with the timid and indolent tortoise.^'' I think we 
may paraphrase this passage by comparing " the active and 
rapacious tadpole " with the timid and indolent frog.''' The 
activity of the tadpole is unquestionable. As for his ra- 
