1896.] ` ` Embryology. 771 
make up for the shortening ef the are by protruding a little from the 
surface of the egg at either end of the furrow. Such a condition is 
admirably shown when one creases the top of a soft felt hat, and would 
necessarily be even more manifest if the hat were filled with a viscous 
An examination of any of the surface views will show that this is 
not the case with these Chorophilus eggs, but that the first indication of 
the groove at either extremity is a slight hollowing in of the surface, 
and not a bulging outward.. This view is confirmed by a study of the 
sections. 
The other alternative is that the shortening of the arc must result in 
longitudinal condensation along the bottom of the furrow, starting at 
the center and increasing as the furrow progresses. 
Such a shortening or contraction along the bottom of the furrow 
would very naturally throw its sides into folds or wrinkles at right 
angles to its length. The pigment layer in contact with these walls 
would also be thickened in the region of the wrinkles, and toward the 
center of the groove. 
Since the condensation starts at the bi tot and advances in both 
directions with the progress of the furrow, the wrinkles would be ar- 
ranged somewhat radially about the superior pole. This progressive 
contraction also accounts for the successive appearance and disappear- 
ance of wrinkles, and for the confluence of smaller into larger ones. 
As the sides of the furrow begin to fuse into the permanent segmenta- 
tion plane or cell-wall the wrinkles disappear through the gradual re- 
adjustment of former relations. 
Indeed, the whole phenomenon seems very largely dependent on the 
rapidity of segmentation and the consequent sudden disturbance of 
normal relations before the IZI portions can adjust themselves to 
their new conditions. 
This fact will serve to explain why the wrinkles show so prominently 
in this particular species, which has a very rapid development, and also 
why the conditions under which they were examined—the transference 
from ice to tepid water and the placing of the eggsin strong sunlight— 
were especially favorable. : 
It may also suggest a reason why one observer has failed to detect 
wrinkles in the eggs of a given species, while another, working under 
more favorable conditions, has seen and described them. And it will 
in a measure account tor the absence of wrinkles on the yolk hemisphere, 
sınce segmentation is very much slower there. 
