J. W. Jenkinson 
173 
were closely packed in rows parallel to the length of the slide, and their axes were 
horizontal, directed across the slide and with their white poles all facing one way. 
In the second series they were spaced and their axes were vertical. As I could 
only hope to have a limited number of eggs cut into sections I thought it best to 
obtain as many as possible under each of these two conditions, that is with both 
pressure and gravity, and without both, and not to attempt to investigate the effect 
of each factor separately. 
In the first series (I) — eggs close, axes horizontal — I have 123 eggs each cut 
into a series of sections, in the second (II) 55 eggs. 
The sections were cut equatorially, that is, at right angles to the axis — and 
therefore also to the First Furrow, since this is meridional — or as nearly as possible 
so. The direction of catting was not, howevei', always exact, and in calculating the 
magnitudes of the several angles, an allowance had to be made for the obliquity of 
the sections to the axis or to both axis and furrow. 
The obliquity of the plane of sectioning to the axis was determined by finding 
the number of sections — the thickness of which was known — intervening between 
the section in which the yolk first appeared and the section in which it appeared 
at a point diametrically opposite. The length of the radius of the egg being 
known, the angle made by the axis with the plane of section may be determined, 
on the assumption, of course, that the egg is a sphere and that the yolk is so 
uniformly distributed around the axis that any plane at right angles to the latter 
would cut equal areas of yolk in all directions from its centre. 
These assumptions are unavoidable, and I think fair. The yolk is normally 
distributed in that way, and I do not think that the spherical eggs become much 
distorted in the processes of preserving and embedding. The same assumptions 
have to be made in calculating the obliquity of the sections to the furrow. This 
was done by counting the sections intervening between the one in which one 
blastomere appears and that in which the other is first seen. In a section at 
right angles to the furrow they would of course appear simultaneously. 
Making these corrections the following angles have been, indirectly, measured. 
(1) The angle between the meridian which includes the point of entrance of 
the spermatozoon and the meridian of the First Furrow. 
(2) By subtraction, the angle between the sperm-entrance meridian and the 
Plane of Symmetry (a meridional plane). 
(3) The angle between the meridian including the end of the first part of the 
sperm-path (' penetration ' path of Roux) and the First Furrow. The former 
meridian I shall call the sperm-sphere meridian because this structure appears at 
the inner end of the path. 
(4) The angle between the sperm-sphere meridian and the Plane of Symmetry. 
(5) The angle between the sperm-entrance radius and the egg axis, or the 
angle subtended at the centre of the egg by the distance between the animal pole 
