EFFECTS ON EGGS OF FRESH WATER PULMONATES 435 
of these cells gave rise to a micromere, two of which were yellow 
and two gray. On the 3d day blastulae had developed, which 
were abnormal in form and distribution of substances. On the 
9th day 17 were normal and had hatched, 2 were abnormal and 
were unhatched, 27 were dead in the gastrula stage. The 2 
abnormal snails showed exostomata, the buccal cavity and radula 
being evaginated, so that the lingual ribbon was spread out on the 
surface (fig. 46). 
Isolations. Five eggs of this lot were isolated in the 2-cell stage. 
Four of these showed the same type of abnormal distribution 
of substances, viz., all the yellow material was contained in a small 
cell, all the gray in a large one. The yellow material was dense 
and finely granular, the gray contained large granules and yolk 
spheres. Blastulae and gastrulae, abnormal in form and dis- 
tribution of colored substances, were formed. Four of these 
isolated embryos died about the gastrula stage ; one lived and on 
the 9th day gave rise to a large normal snail, which hatched from 
the capsule. In the early stages there was no evident difference 
between the eggs which did not develop beyond the gastrula and 
the one which did. 
Experiment 20. Eggs in the germinal vesicle stage were cen- 
trifuged slowly for 4 hrs. up to the time of the first cleavage, at the 
close of which time the separation of substances was very com- 
plete and the eggs much elongated. On the 4th day abnormal 
and irregular gastrulae had formed; on the 5th day ciliated em- 
bryos were present and rotating; on the 7th day veligers had 
formed and looked approximately normal; on the 16th day none 
had hatched and all were very abnormal. 
Experiment 21. Centrifuged 10 min. in the 2-cell stage. The 
early cleavages were normal in form, although not in the distri- 
bution of substances. All had died on the 2d day. 
Experiment 22. Centrifuged 10 min. in the 2-cell stage. The 
cleavages were very abnormal in form and in distribution of sub- 
stances; the blastulae and gastrulae were parti-colored and irreg- 
ular in form; and all had died on the 5th day. 
These experiments are briefly summarized in the tables on 
the pages following. 
