434 
EDWIN G. CONKLIN 
cleavage was abnormal, and the form of the cleavage, blastula 
and gastrula was generally abnormal (figs. 32, 33). On the 11th 
day 8 young snails were nearly normal but unhatched, 3 were 
very abnormal and unhatched, 15 had died about the stage of the 
gastrula. Two of the 8 nearly normal snaDs had conical shells 
with the apex turned forward and to the right (fig. 47) ; whereas 
in normal Physas it turns back (posteriorly) and to the left. 
Experiment 16. Cen+rifuged 12 min. after the formation of 
both polar bodies and before the first cleavage. After centri- 
fuging the eggs became elongated and the subsequent cleavage 
was frequenth^ very abnormal in form as well as in the distribu- 
tion of substances. The blastulae and gastrulae were generally 
abnormal in form; on the 8th da}^ all of 25-30 embryos were 
dead except 4. 
Isolations. Thirteen of these centrifuged eggs were isolated 
in the 2-cell stage for various abnormal distributions of substances, 
and all of them died about the gastrula stage. 
Experiment 17. Centrifuged 12 min. after the extrusion of 
both polar bodies. The stratification of substances was dis- 
tinct, but the eggs did not elongate as in Exp. 16. In the 2-cell 
and 4-cell stages the distribution of the yellow and gray sub- 
stances was ver^^ abnormal (as in figs. 32-33). On the 10th day 
3 young snails had hatched and were quite normal, 1 was unhatched 
but nearly normal, 2 were unhatched and very abnormal and 27 
had died about the gastrula stage. 
Experiment 18. Centrifuged for 2 min. after the formation 
of the polar bodies and before the first cleavage (exact age un- 
known). The separation of the egg substances was not very dis- 
tinct. On the 10th day 22 3^oung snails had hatched, 17 had not 
hatched, and 43 had died about the gastrula stage. 
Experiment 19. Centrifuged 5 min. just before tne first cleav- 
age of the egg. The gray substance was in all cases more abund- 
ant than the yellow, and in all cases in which the distribution of 
these substances to the first two blastomeres was unsymmetrical 
the yellow cell was smaller than the gray (as in fig. 32). At the 
4-cell stage of many eggs, two cells were small and yellow, while 
two were large and gray (as in fig. 33). At the 8-cell stage each 
