58 
L. Kaufman : 
I 1 '; 
of the larva, phot. 4 a similar section of an animal transformed after 
two weeks’ feeding on thyroidine (same enlargement). The differ¬ 
ences observable on these photographs are enumerated in the fol¬ 
lowing synopsis. 
Thyroid gland of the 
larva. 
The quantity of connective 
tissue which surrounds the gland 
is considerable. 
The diameter of the glandul¬ 
ar vesicles attains 20 to 180/4. 
Few capillary vessels. 
The glandular epithelium 
consists of cylindric cells, about 
13 /4 in height; their nuclei.are 
globular or somewhat elongated. 
The epithelium forms intra- and 
interfollicular outgrowths. 
Not all the vesicles are filled 
with colloid. The colloid of 
many vesicles is only feeblv 
stained by eosine. 
The structure of the thyreoidea described in the above is similar 
to that of the thyreoidea of neotenic larvae visible in Adler’s 
photographs (see a paper by this author on the influence of temper¬ 
ature and on the influence of hypermaturity of eggs on metamor¬ 
phosis). Adler’s photographs and phot. 3 of the present paper 
show that a direct connection exists between neotenia and the 
structure of the thyroid gland. Thyreoidea of neotenic forms contains 
vesicles smaller than those of the normal larvae, with high epithe¬ 
lium, forming intra- and interfollicular outgrowths. Some of the 
vesicles are not filled with colloid, others contain colloid which 
becomes only feebly stained by eosine; according to Adler, this 
proves that it is abnormal. 
Thyroid gland of the 
transformed specimen. 
The quantity of connective 
tissue has diminished. 
The vesicles have increased; 
the smallest diameter 70 / 4 , the 
largest about 250 /4. 
Capillary vessels numerous. 
The cells of the glandular 
epithelium are flat, about 2 (i 
in height; long nuclei surrounded 
by a small quantity of plasma. 
No intra- or interfollicular out¬ 
growths. 
All the vesicles are filled 
with colloid which is strongly 
coloured by eosine. 
