368 FRANK R. LILLIE 
stages of maturation and fertilization. This is Meves’ modifi- 
cation of Flemming’s fluid made as follows: chromic acid, 0.5 
per cent, 15 cc.; osmic acid, 2 per cent, 3.5 cc.; glacial acetic 
acid 3 drops. The eggs were left in the fluid from thirty to forty- 
five minutes. Fixation in this fluid causes no shrinkage, the oil 
is so changed that it is not dissolved out by subsequent imbedding 
in paraffine; the sections stain beautifully 1n iron haematoxylin, 
and certain substances are clearly differentiated which can be 
detected only with the greatest difficulty after fixation in any 
other fluid tried. 
a. The penetration of the spermatozoon. It was noted in the first 
part of this paper that a single spermatozoon becomes attached 
to the egg-membrane immediately after insemination, and that 
the breaking down of the cortical layer, secretion of the jelly 
and formation of the perivitelline space follow immediately, 
though the actual penetration of the spermatozoon is delayed 
forty or fifty minutes. 
The act of penetration involves no motile activity on the part 
of the spermatozoon; after the latter has become attached to the 
vitelline membrane all movement of the spermatozoon ceases 
and it remains absolutely immotile throughout the forty or fifty 
minutes that elapse before it is taken into the egg. The events 
of this period as seen in the living egg are as follows: 
1. The jelly is formed by outflow of the alveolar contents of 
the cortical layer-as already noted; although a large amount of 
jelly is formed in two or three minutes, yet the process lasts ten 
or fifteen minutes before the deeper alveoli are emptied. There 
is then a very wide perivitelline space crossed by the alveolar 
walls which are attached to the plasma membrane, presenting a 
very striking appearance (fig. B). 
2. The protoplasm of the egg immediately beneath the at- 
_ tached spermatozoon then forms a rounded elevation, the entrante 
cone, which gradually moves across the perivitelline space and 
comes in contact, and fuses, with the membrane (fig. B, a). This 
condition is usually fully attained about fifteen to seventeen 
minutes after insemination. 
