EFFECTS ON EGGS OF FRESH WATER PULMONATES 427 
with the gray and yellow zones by this time, so that the distinc- 
tion between them was not so sharp as at first. The eggs still 
oriented with the gray pole up, the j^ellow pole down and with the 
polar bodies on the surface between the two. However, before 
the first cleavage, which occrrued about 2 hrs. after the formation 
of the second polar body, the clear zone was but faintly distin- 
guishable from the gray and yellow and the eggs no longer oriented 
rapidly as they did earlier. The axis connecting the gray and 
yellow poles (axis of stratification) may lie at any angle with re- 
spect to the first cleavage plane, and consequently the gray and 
yellow substances maybe distributed equally to the first two blasto- 
meres or all the gray may go into one of these blastomeres, and 
all the yellow into the other, or all degrees of unequal distribution 
of these substances may occur. This uns^^mmetrical distri- 
bution of gray and yellow material could be recognized at all 
stages of the cleavage and gastrulation; however, the form of the 
cleavage, the gastrula, and the veliger were entirely normal, and 
every egg of this lot, without exception, gave rise to a perfectly 
normal snail. 
Nine eggs of this lot were isolated in the 2 and 4-cell stages ; 
all of these showed abnormal distribution of the gray and yellow 
substances and yet every one of them gave rise to a normal snail. 
Experiment 3. Eggs of Lymnaea, in the germinal vesicle stage, 
but some time after being laid, were centrifuged for 10 min. The 
stratification of substances, orientation of eggs and place at which 
the polar bodies were extruded was the same as in the preceding 
experiments. In the gastrula stage, however, some were seen to 
be abnormal in form as well as in the distribution of the gray and 
yellow substances, and after 14 days 11 were abnormal or dead, 
while 46 were apparently normal. 
Experiment 4. Eggs of Lymnaea in the germinal vesicle stage 
and about 1 hr. before the formation of the first polar body, 
were centrifuged, full speed, for 20 min. The separation of 
the substances was very sharp, the relative quantities being 
about as follows: gray one-eighth, clear three-eighths, yellow 
one-half. The germinal vesicle always remained in the clear 
zone, though it sometimes encroached a little upon the yel- 
THE JOURNAL OF EXPERIMENTAL Z05L0GT, VOL. 9, NO. 2. 
