396 The American Naturalist. [April, 
The first four cells are thus all alike in their possibilities as well as 
in appearance ; not so the first eight cells, though they all look alike. 
When the eight cells are separated into groups of four these give 
rise to quite different sets, some with eight large, others six large and 
two little cells, others four large and four small cells. Thus the devel- 
opment of the eight cell stage is largely a process. of “self differentia- 
tion ” of these cells and not due to the mere interaction of the cells of 
the group. 
By destroying one of the first two cleavage cells half-blastulas even, 
perhaps, half-gastrulas were reared in a few cases from the single 
remaining cleavage cell. The half-blastulas were obtained both after 
piercing and removing one cell and by killing it by shaking, which 
left it still inside the intact membrane. 
The half-blastulas showed a tendency to close in as spheres, but died 
first. 
One interesting case suggesting Roux’s “ postgeneration ” was seen, 
but lost. It consisted of a half blastula lying against a second solid 
hemisphere covered over by a layer of cells continuous with the half- 
blastula. 
Electricity and Cleavage.—Wilhelm Roux,’ seeking to deter- 
mine if electrical phenomena are involved in the process of karyoki- 
netic cell division, subjected frogs’ eggs to the action of a current from 
three Bunsen cells. In these experiments, made in 1885‘, the eggs 
were placed in a glass tube surrounded by the coiled wire conveying 
the current. : 
The result was negative. In the present paper the author describes 
the results obtained by the use of an alternating current of 100 volts 
or less, used for lighting the Anatomical Institute at Innsbruck. Here 
again, the result as far as any connection of cleavage or cell division 
and the electric current is concerned, was entirelyfnegative. When 
the current was not strong enough to kill the eggs they divided in the 
glass tube without any reference to the presence and direction of the 
current. The same is found to be true of the maximum continuous as 
well as of the alternating current. 
The alternating current is also found to have no directive effect upon 
the entering sperm or the fusing pronuclei, factors which Roux regards 
as determining the first cleavage plane. The electric current has, 
` however, a marked effect upon the egg, visible as a change in color at 
5Bresl. ärzt. Zeitschrift, 1885, No. 6. 
‘Sitzb. Akad. Wiss. Wien., Jan., 1892. 
