370 FRANK R. LILLIE 
the complete retraction of the entrance cone, is about twenty-two 
to twenty-five minutes after fertilization (fig. B, b, ¢, d). 
4. The perivitelline space then narrows around the entire 
egg, and the depression of the membrane in which the spermato- 
zoon is seated disappears; in consequence, the spermatozoon 
again becomes prominent externally. 
5. It remains prominent for ten or fifteen minutes (about 
forty to fifty minutes after insemination), and then disappears 
rather abruptly within the egg as though some resistance had 
given away. Its penetration coincides with the late anaphase of 
the first maturation division; in a few cases it may be a little 
earlier or a little later. 
The egg is changing form at this time and in consequnce the 
perivitelline space is often widened locally, especially in the ani- 
mal hemisphere; if this happen in the region of penetration, which 
may be any part of the egg, strong cytoplasmic strands are drawn 
out between the membrane of the egg and the point of penetra- 
tion, showing that the egg membrane and the cytoplasm are 
actually fused here. 
To repeat and extend the observations on the living egg several 
series of eggs were preserved every five minutes from the time of 
insemination in Meves’ fluid. The study of thesections confirmed 
and extended the above observation on the living egg as follows: 
Ten minutes after insemination the entrance cone is quite 
well formed and the spermatozoon is clearly seen outside, separ- 
ated from the entrance cone only by the thickness of the vitelline 
membrane with which it is in contact. 
Fifteen minutes after insemination essentially the same con- 
dition persists. ‘The entrance cone is homogeneous, shading off 
into the surrounding yolk-filled protoplasm. It stains very dark 
in iron haematoxylin. The head of the spermatozoon appears 
exactly as before. 
Twenty minutes after insemination the entrance cone has flat- 
tened out, but the spermatozoon is still external to the membrane. 
The substance of the entrance cone is, however, as readily recog- 
nized as when it projected above the surface of the egg. 
