NATURAL HISTORY OF AMERICAN LOBSTER. 
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the lobster, but its eggs are occasionally straw color, grayish-green, or yellow-green. 
When plunged in alcohol or hot water the ova respond like the shell of the animal and 
become light red, a more stable pigment, a lipochrome, soluble in alcohol, being formed. 
By adding alternately hot and cold water the eggs may be turned to red and green 
several times in succession. 
The fresh-laid eggs, which are seldom seen, can be detected by examination with a 
hand lens. The transparent capsule closely invests the yolk, which presents a very 
fine-grained and uniform texture, quite different from that which the ova later possess. 
Maturation is without doubt completed by the formation of polar cells either in the 
ovary or during the passage of the eggs to the outside, although we have never been 
able to find these bodies in stained sections of the egg. External segmentation of the 
yolk follows in from 20 to 25 hours after oviposition, and the large yolk segments which 
are early formed can be detected by the naked eye. A clear perivitelline space, 
apparently filled in part with exudatian from the egg, soon appears between the shell 
and yolk. At the close of this process, or after invagination has begun, the living egg, 
when examined with a hand lens or low power of the microscope, is likely to be mis- 
taken for one freshly laid. The ova, however, are not so closely adherent, are somewhat 
lighter in color, and the yolk has a coarser and more irregular texture. The first division 
of the protoplasm is central or subcentral. In the second and third segmentations, 
with four and eight cells, the products begin to separate and migrate outward. The 
greater number tend to move toward the side which marks the animal pole, where the 
yolk becomes distinctly flattened, and the shell correspondingly elevated. The cells 
which migrate toward the surface of the depressed area bring about the first segmenta- 
tion of the yolk into hillocks. As they multiply by indirect division their products 
diffuse over the egg, and at the fifth segmentation, of 32 cells, the entire surface of 
the yolk is thrown into hillocks or inverted pyramids. The segmentation is rythmical, 
the early periods lasting about 4 hours, but the rythms of individual cells are not 
in harmony, and the segments are unequal. Later when about no cells are present 
the periodic divisions become more uniform over the entire egg. With each division 
the protoplasm approaches nearer the surface, and meantime a limited number of cells 
are formed by tangential divisions and migrate to the depths of the yolk. By a con- 
tinuation of this process the yolk becomes surrounded by a thin mosiac of cells, or 
rather by a single tier of several thousand minute columnar cells or diminutive yolk 
pyramids of uniform size. Their “apices” blend into the central yolk mass, which 
harbors a few wandering and degenerating cells. 
Cell division then becomes more rapid over a considerable area of the surface, 
which includes the animal pole, and at a certain point an invagination of superficial 
cells occurs. This begins by the in-wandering of a few cells, and is followed by the 
rapid multiplication of those thus immersed in the common food stock of the developing 
egg, and by the sinking of a small area of the blastoderm about this point, forming what 
is usually called the “egg gastrula” stage. The depression is at first shallow, and 
becomes a well-defined circular pit, but is never very deep. It is subject to marked 
