430 FRANK R. LILLIE 
The eggs preserved immediately after centrifuging enable one 
to study the immediate effects of the separation of the jelly on the 
spermatozo6n, and those preserved later show what portions of 
spermatozoa remaining attached after centrifuging have entered 
the egg and what their fertilizing power has been up to the time of 
preservation. Some of the eggs were kept living for estimation 
of the per cent of eggs that undergo segmentation (last column). 
In other experiments the eggs were preserved at different periods 
following centrifuging, because no single experiment gives a suffi- 
cient quantity of material for preserving a complete series of 
stages. In this way from a considerable number of experiments 
a& very complete set of stages was secured. 
Each lot of eggs preserved included several hundred which were 
embedded together in paraffine and cut in serial sections which 
would usually cover four or five slides under a 50 by 25 mm. 
cover, if all the material were cut. On one such slide I estimated 
by counting that there were 374 eggs present; and the 1911 mate- 
rial alone made 376 slides. Only about a fourth of the slides 
contain the desired stages, and the figures are given only to show 
‘that a large quantity of material has actually been under review to 
give the results. However, I may say that figs. 18 to 23 are all 
from a single slide, and other interesting stages occurred on the 
same slide; it is possible in fact to demonstrate the whole set of 
phenomena from a few slides of the large number prepared. 
The clew to the whole set of phenomena was given by the dis- 
covery of very minute sperm nuclei in the material used for the 
second of these studies (F. R. Lillie, ’11). In the effort to dis- 
cover the origin of these minute, and presumably partial, sperm 
nuclei, the whole history was gradually worked out as given here. 
The centrifugal force employed causes a very complete segre- 
gation of the oil and granules of the egg into four zones which are 
illustrated in text fig. 3, taken from a section fixed in Meves’ 
modification of Flemming’s fluid and stained in iron haematoxylin. 
These zones are, beginning with the constituents of least specific 
gravity; (1) the zone of the oil drops; (2) the hyaline zone in which 
the smaller basophile granules gather for the most part; (3) the 
zone of the yolk-spheres; (4) a zone consisting of small hyaline | 
