108 THE AMERICAN NATURALIST. 
denser, while in the case of Hydra, the lightest, the extreme 
vacuolation of the inner layer may well indicate a less repre- 
sentative character of the protoplasm. 
In the case of the developing animal the chief tissue to 
absorb water, and, therefore, the tissue of most rapid increase 
in bulk, is the mesenchyme. All of the walls of the internal 
organs, however, grow thinner and less dense as the animal 
increases in size. 
This work has been carried on under Dr. Charles B. Daven- 
port, whose suggestions are the basis of anything of value it 
may contain. 
PAPERS CITED. 
DAVENPORT, C. B. 
'97-99. Experimental Morphology. xvii + 508 pp., 140 cuts. New 
York, The Macmillan Company. 
GALLOWAY, T. W. 
'98. Effect of Temperature on Growth of Tadpoles. Science. Vol. 
viii, N.S., No. 189, p. 178. [Abstract.] 
LANDOLT, H., UND BORNSTEIN, R. 
'94. Physikalisch-Chemische Tabellen. Zweite Auflage, xi + 563 pp- 
Berlin, J. Springer. 
PLATT, JULIA B. 
'99. On the Specific Gravity of Spirostomum, Parameecium, and the 
Tadpole in Relation to the Problem of Geotaxis. American 
Naturalist. Vol. xxxiii, No. 385, pp. 31-38. 
