598 
T. H. MORGAN 
lots the eggs developed well. Here at last was a clue for further 
examination. Something in the handling of the eggs after they 
had been laid may have caused them to develop abnormally. I 
put some eggs in one of the centrifuge tubes and turned the 
handle only five times very slowly. This sufficed to throw most 
of the eggs to the bottom of the tube. As a control, eggs of the 
same individual centrifuged 25 turns were used. Without excep- 
tion all went abnormall3^ Here the eggs had only been centri- 
fuged by five turns of the handle, yet were injuriously affected. 
The result showed that something else than the centrifuging was 
responsible for the results. 
Experiments with the eggs of the sea-urchin had shown me 
that if the eggs are thrown down suddenly on the centrifuge the 
membranes may be destroyed. The presence of a few drops of 
gum arable (in sea water) at the bottom of the tubes prevents the 
eggs from becoming closely appressed and also helps to keep the 
membranes intact. I allowed eggs of Cumingia slowly to settle 
to the bottom of the centrifuge tube in which a drop of gum arable 
had previously been placed. But in order to get the eggs out of 
the tube the}^ must be rather roughly treated. Six lots so handled 
centrifuged only six turns, gave abnormal embryos. The gum 
arable was a rather thin solution in the last experiment and the 
eggs sank into it. Thicker gum was used and the eggs removed 
carefully. All six lots developed normally. The gum solution 
was again used in six lots and abnormal embryos developed. 
If, as the experiments indicate, the eggs are damaged by the re- 
moval of the membranes, the same results should follow if, instead 
of centrifuging, the eggs are simply squirted in and out of a 
pipette. Six separate lots, so treated, gave only abnormal 
embryos. 
Eggs were allowed slowly to sink in the centrifuge tubes and 
were then roughly squirted out. They went abnormally. The 
controls were normal. Other eggs roughly handled also went 
abnormally. 
These experiments show plainly enough that abnormal develop- 
-ment is brought about by any handling of the eggs that is a little 
rough. The most plausible explanation is that such treatment 
