Isolated Blastomeres of the Frog’s Egg. 427 
through which the remaining part of the blastomere could be 
extracted. The eggs of Chorophilus were more easily handled, 
since the jelly was softer and the egg itself did not collapse readily. 
This egg is not so small as to make operations difficult with the 
low power of the binocular microscope. 
When the first cleavage furrow had extended almost around the 
egg, the greater part of the jelly was carefully removed with filter 
paper and the puncture made. The egg was then allowed to rest 
until the first cleavage plane had completely divided it. At this 
time the remains of the punctured blastomere were removed 
with the capillary pipette. In case the last remnants could not be 
removed, the egg was allowed to rest again until the remnants of 
the punctured blastomere turned pale, which was an indication that 
they were more brittle and could now beremoved with a fine needle. 
When the egg was punctured, the perivitelline space was oblit- 
erated by the escape of the contained fluid and the jelly pressed 
close to the egg, an opening was also made through which bacteria 
might enter; therefore, the eggs laid in the laboratory under a 
more sterile condition, gave better results than those laid in the 
ponds. Care was taken to keep the egg normally orientated in 
reference to the direction of gravity both during and after the 
operation. 
The operated eggs were observed with the binocular micro- 
scope and the early cleavage noted. The gastrulation was watched 
through the sides and bottom of the glass dishes in which the eggs 
were kept. After the embryos became ciliated, some of them 
turned in a normal manner so that they could be observed in all 
aspects, from above: 
A-large number of eggs of both Rana pipiens and Chorophilus 
triseriatus were operated on. All of the former died, but of the 
latter a considerable number gastrulated and several reached the 
tadpole stage. Two were four days, three were five days and one 
was eight days old when preserved for sectioning. 
The control eggs hatched in less than eight days, but the operat- 
ed eggs were retarded in development and the resulting tadpoles 
were too weak to break through the jelly, although the twitching 
of their tails showed that the'muscles were functional. 
