210 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
however, again becomes less, and the eggs once more rise to the surface. Not all of 
the eggs suffer this chauge iu si)eciflc gravity. lu the batch from which my material 
was taken not more than two-thirds sank, the time beiug about forty hours after 
fertilization. 
My material was obtained in the first days of June, when the temperature of the 
water was 00° P. The time from fertilization to hatching was about seventy-five hours. 
Later iu the mouth, of course, the time was considerably less. The percentage of fish 
hatched out was very large, and for three or four days after hatching the young fish 
kept in aquaria remained in good health. By that time the yolksac had almost 
entirely disaj)peared, and the now very active fry evidently needed more spacious and 
varied quarters, for they began to die at a great rate. 
In sectioning I found that the eggs killed iu Perenyffs fluid, both old and young 
stages, yielded the best results. The yolk never becomes hard, but is coagulated, and 
especially in the young stages (segimmtation and formation of the periblast) contracts 
away from the blastoderm, which it is therefore easy to separate from the yolk by 
means of needles. 
After the body of the fish is once well outlined, I find it is better not to section the 
whole egg, but with flue scissors to cut off the embryo, and if possible shake it free 
from the egg membrane. With a little care the whole body may be obtained unbroken 
and entirely free from yolk, and yet with the periblast layer attached. 
For surface imeparations of the blastoderm during the stages of segmentation and 
formation of the periblast, the Perenyi embryos mounted iu balsam answered fairly 
well. But much better preparations were obtained by killing the eggs in acetic acid, 
or in osmic and acetic, and mounting the embryos directly in glycerine. 
I take this opportunity of thanking the Boston Society of Natural History and its 
librarian. Dr. J. W alter Fewkes, for the extremely obliging manner in which they have 
sent to Wood’s Holl whatever books and journals I have asked for. 
There are already several monographs in which the growth of our knowledge of 
Teleost development has been traced with great care, and I have therefore not con- 
sidered it necessary to givm extensive historical reviews. Hoffman’s long paper (17) 
especially contains a full account of past work, and Heuneguy’s “ Embryogenie de la 
Truite” (1888) brings the record nearly up to the present date. 
I. SEGMENTATION. 
The egg of the Sea Bass is a small pelagic egg about 1 millimeter in diameter. 
The egg membrane is thin and horny, but even after mouths in alcohol does not grow 
very hard. The yolk forms a single translucent sphere which, after coagulation of 
the albumen, shows in sections a finely reticulated structure. Imbedded in the yolk, 
but near the surface, is a single large oil globule, which is always uppermost in the 
floating egg. In the ripe unfertilized egg the yolk is covered by a thin layer cf proto- 
plasm, of about the same thickness at all points. Shortly after fertilization this dif- 
fused protoplasmic layer begins to concentrate towards a point just opjiosite the oil 
globule. The ‘‘ streaming ” of the protoplasm, which characterizes the concentration, 
has been well described and figured by Eyder for the Cod (34). A couple of hours 
after fertilization there is found at the lower pole of the floating egg a disk of proto 
plasm, lenticular in section. At its edge the disk thins away into an excessively thin 
