124 University of California Publications in Zoology [Vou.9 
the granules are apparently single or in clusters of various sizes 
pretty uniformly distributed. They seem, under an oil immer- 
sion, to be more or less angular. In eggs of the rat, oh the other 
hand, the granules are not so clean cut and brilliant, and before 
maturation is complete they are arranged irregularly. The egg 
has a somewhat mottled appearance, as though the granules 
formed a very coarse network. After the second polar cell is 
formed, this appearance is lost and the distribution of the 
granules is quite uniform. 
Nothing whatever can be seen in the living egg of nuclear 
or spindle figures. 
The eggs of both animals are approximately of the same size. 
Since salt solutions of slightly different density cause variations 
in the size of the eggs exact figures cannot now be given. 
The first polar cell of the mouse egg was present in most of 
the eggs observed. It is large and very conspicuous and its 
eytoplasmie contents are very similar to the egg cytoplasm. It 
is more or less spherical, sometimes flattened, at times clearly 
amoeboid, lightly in contact with the egg or situated in a shght 
depression in the surface of the egg. The amoeboid condition 
may well account for the change in position described by several 
writers. When fixed, the zona is caused to contract quickly into 
eontaet with the cytoplasm and the polar cell to be rather deeply 
pressed into the egg. No second polar cell has so far been 
formed under the microscope, even when active spermatozoa are 
introduced into the artificial fluid. 
In the rat the first polar cell is much less conspicuous. It is 
smaller and may easily be overlooked. 
It has been possible to seminate rat eggs with rat spermatozoa 
and to observe the formation of the second polar cell. For- 
tunately the eggs always lie in such a position that the forming 
polar cell can be seen in profile. The formation, usually near 
the first polar cell, may begin within five minutes to two or 
more hours after the spermatozoa are introduced. The con- 
striction may be finished three-fourths of an hour later. The 
process is strikingly like that described (Long and Mark, 1911) 
for the mouse egg as far as the external features are concerned. 
The first appearance is an elevation clearer than the rest of the 
