L. Kaufman: 
44 
fed on thyroidine. We see that only after several days a rapid 
decrease of weight sets in which continues even after we cease 
giving thyroidine and abundantly feed the specimens on meat. 
The curves of the weight of axolotls fed on thyroidine fully cor¬ 
respond to those of the weight of tadpoles undergoing metamorphosis, 
given in S chap er’s paper. Sch a per ascertained that the loss 
of weight for the most part consists in loss of water. Feeding on 
thyroidine probably also causes a decrease of osmotic tension 
connected with loss of water. This assumption is confirmed by the 
observation of the structure of the tissues of axolotls experimented 
upon, to be described below. The behaviour of a normally fed 
axolotl, which was put alternatively into shallow and deep water, 
shows that oscillations in the animal’s weight depend in great part 
upon the quantity of water contained. When an axolotl is put into 
an aquarium where it is only partly covered with water, the animal 
becomes lighter and its fin undergoes resorption; brought again 
into deeper water (even if not fed), it weighs more than in shallow 
water. These variations are shown in the curve No. 4. 
The resorption of gills and of the fin sets in at a time when the 
animal begins to become thinner, i. e. when a decrease of weight 
becomes noticeable, or even somewhat earlier. Maeroscopically we 
may only observe diminution of length and breadth of the gill- 
trunks and filaments, and a gradual, uniform atrophy of the fin; 
in albinotic specimens also hyperaemic spots in the fin. Under the 
magnifying glass we see abundant blood-circulation in the respiratory 
organs undergoing resorption. I found that blood still circulates, 
even in small fragments of gill-trunks which are to be seen for 
some time in almost entirely transformed terrestrial specimens. 
Loos considers the deficiency of blood-circulation to cause 
degeneration of the tail in tadpoles, when metamorphosing. I venture 
to say, I cannot agree with that opinion. As parts undergoing 
resorption are abundantly supplied from the blood, deficiency of 
blood-circulation cannot be considered to be the primary cause of 
resorption. The following opinion expressed by Wintrebert 
seems to me to approach the truth: „II ne semble pas justifié 
d’admettre, comme cause de la régression caudale, un trouble cir¬ 
culatoire local ou général. On observe pendant la métamorphose 
une circulation très active de la queue, et non un moindre apport 
