100 THE AMERICAN NATURALIST. [Vor. XXXIV. 
cross-sections from tadpoles of Rana silvatica at different ages. 
They are in black and white, all solid cell tissue being printed 
black. They are all outlined with the camera to a magnifica- 
tion of 30 diameters. 
As nearly as possible they are from corresponding regions of 
the body— the region just back of the thickened auditory epi- 
thelium. No.1 is taken from a specimen 
2% mm. long. 
Plainly there are here very few spaces 
which may contain water or lymph. The 
cells also are very crowded and show no 
vacuolation. 
No. 2 is from a 10 mm. tadpole. The 
change is remarkable, especially in the de- 
velopment of the highly vacuolated mesen- 
chyme. The neural canal is larger, while 
n the cross-section of nervous tissue is not 
magnified 30 diam.; tis- greatly increased. 
al meio MN The cavities of the cesophagus, intestine, 
and liver are large, and the pronephric tubules also increase 
the interior space. 
As the best example of the 
change in individual cells, I call 
attention to those of the chorda, 
which are very strongly vacuo- 
lated. 
The cross-section (Fig. 3) 
from a 20 mm. tadpole shows 
that, except for the cluster of 
cells on the right which forms 
the limb bud, the area of solid 
tissue has decreased greatly. 
The epidermis is very thin com- Fıs. 2. — Cross-section R. silvatica, 10 mm. 
pared to either of the other v ——ÀPHÀ 
examples, and the cesophagus and intestinal wall are not more 
than half as thick as in the preceding stage. 
Table V shows that the actual tissue (dry weight) in speci- 
men No. 2 must have been less than in No. r. That the actual 
