420 
EDWIN G. CONKLIN 
OBSERVATIONS 
My own observations on the nature and movements of the egg 
substances of puhnonates are not very different from those of 
Brooks, Rabl and Mark. In 1902 I spent several weeks in the 
study of the phenomena of maturation, fertihzation and cleavage, 
as they may be seen in the living eggs of these animals. In the 
main these observations were confined to the eggs of Physa hetero- 
stropha, Lymnaea columella, and Planorbis trivolvis. In all of 
these the phenomena observed are essentially alike and, unless 
otherwise specified, it may be assumed that the following account 
applies to all the species named. 
At the time the eggs are laid there is a large spherical germinal 
vesicle in the egg, which is quite transparent, whereas the rest 
of the egg is rather opaque from the presence of yolk granules and 
a diffuse yellow pigment, which is uniformly distributed through- 
out the egg (fig. 1). At this stage there is no evident distinction 
between the substances at the animal and vegetative poles. The 
germinal vesicle is slightly eccentric toward one pole, but neither 
at this stage nor at any subsequent one do the eggs orient them- 
selves with respect to gravity, consequently they lie in the jelly 
masses with their chief axes in almost every possible direction. 
As the germinal vesicle begins to dissolve and the first matura- 
tion spindle appears the clear area of the germinal vesicle becomes 
elliptical and then spindle-shaped in outline. This clear area 
then moves through the egg until one end of the elongated area 
comes into contact with the surface at the animal pole of the egg, 
leaving a deep ^^well" of clear protoplasm leading down to the 
center of the egg (fig. 2). Close around this clear protoplasm is a 
finely granular yellow substance which is quite distinct from the 
yolk on the one hand and the clear protoplasm on the other. As 
the first maturation division advances this ''well'' grows shal- 
lower and the clear protoplasm is spread out on the surface as a 
cap at the animal pole (figs. 3, 4). This cap is pearl gray or milky 
in appearance when seen by reflected light, or when brightly 
illuminated by transmitted daylight; it will be referred to as the 
clear protoplasm or substance. 
