1895.] Microscopy. 511 
would reward the investigator of this subject who first mastered the 
language and then gained the confidence of these people. 
—H. C. MERCER. 
The Potters’ Wheel in Yucatan.— While in charge of the Cor- 
with Expedition of the University of Pennsylvania in Yucatan last 
month (March, 1895), and while studying the process of pottery making 
by modern Maya Indians at Merida, I saw a female potter reproduce 
the chief conditions of the potters’ wheel by turning a wooden disc set 
on a board with her toes. The clay rested on the disc and received the 
impress of her tools and fingers while revolving. Though the disc was 
called, in Maya, Kabal, it may be doubted whether it is an inheritance 
by these Indians from their pre-Columbian ancestors and not derived 
from Spain ; in other words, whether its present use demonstrates the ex- 
istence, till now undiscovered, of the potters’ wheel in ancient America. 
Doylestown, April 13, 1895. —H. C. Mercer. 
MICROSCOPY.’ 
Cytotropism of Cleavage Cells.’—The principle of the method 
employed by Roux is very simple; but the experiments require to be 
carried out with care, in order to exclude as far as possible sources ot 
error. a 
The eggs of Rana fusca, obtained from newly captured animals at 
the beginning of the normal period of spawning, furnished the best 
material for observation. Eggs obtained from animals kept separate 
and thus prevented from spawning at the normal time, proved to be 
quite unsatisfacto 
The phenomena of cytotropism are seen most readily between cells 
separated from the egg in the morula or blastula stage. The separa- 
tion is effected by cutting or tearing the egg in an indifferent fluid, 
such as the white of a hen’s egg, or a } per cent salt solution. 
One requires for such experiments a small quantity (5-10 cem.) of 
freshly prepared white of egg each day. This is prepared by filtering, 
in an uncut state, through a wad of cotton. The preparation must be 
perfectly clear. 
The egg, in the morula or blastula stage, is first stripped of its gelat- 
tinous envelope, and placed on a circular glass plate, about 3 cm. in 
1 Edited by C. - Plaga University of Chicago. Contributions should be 
addressed to the edi 
? Wilhelm Roux, Ach. f. Entw’mech. d. Organismen, I, 1, pp- 44-48. 
