BIGELOW: EARLY DEVELOPMENT OF LEPAS. 69 
and finally results in a telolecithal arrangement of the materials of the 
egg. 
Eggs taken from the egg-lamellz at all phases of the maturation have 
been carefully compared with the corresponding stages of isolated eggs 
which were kept in watch glasses. The distortions in form produced by 
pressure apparently do not disturb the normal course of cytological 
changes in the egg. 
Figures 1-6 represent a séries of camera sketches made from a living 
egg at intervals within a period of three hours. In Figure 1 the egg is 
represented just at the completion of the separation of the second polar 
cell. The egg is approximately spherical and closely surrounded by the 
vitelline membrane (mb.vt.). The yolk with its oil globules is in general 
uniformly distributed, but already some of the globules have been seen 
to move towards the vegetative pole. Figure 2 shows the well-marked 
beginning of elongation ; the yolk is collecting at the vegetative pole and 
a mass of protoplasm, concentrating into the animal half of the egg, is 
dark and granular. Figure 3 represents a stage some minutes later. A 
circular depression has appeared around the egg at the equator constrict- 
ing the egg into nearly equal lobes. The upper, protoplasmic lobe is dark 
and granular, especially near its centre, whereas the lower or yolk-lobe is 
relatively clear and transparent, as represented in Figure 18 (Plate 2). 
The constriction now moves toward the vegetative pole of the egg, where 
the yolk is collecting (Fig. 4). Gradually the constricting furrow dis- 
appears (Fig. 5), and the egg becomes ellipsoidal, as shown in Figure 6. 
At the animal pole the egg continues to be bluntly rounded, while at the 
vegetative pole it becomes more pointed. The vitelline membrane, hay- 
ing taken on this shape, retains it throughout the development, and 
appears to be quite rigid from this stage onward. At the close of the 
elongation the upper, animal portion of the egg is largely composed 
of dark granular protoplasm containing some small granules of yolk, 
but no oil globules (Plate 2, Figs. 19, 20). The lower vegetative 
part of the egg is more transparent and contains the mass of yolk gran- 
ules. The oil globules are concentrated at the pointed end of the egg 
and for a time are arranged in strict radial symmetry with respect to the 
long (chief) axis of the egg. Protoplasmic strands extend throughout 
the vegetative half of the egg. 
The elongation of the egg and the separation of yolk and protoplasm, 
which result in the telolecithal condition and the establishment of visible 
polarity, are entirely distinct from the first cleavage processes, with which 
Groom (’94) has confused them (see review of the literature on first 
