NATURAL HISTORY OF AMERICAN LOBSTER. 
311 
Before the question of egg attachment in the crab can be settled we must have very 
full and exact observations of the behavior of these animals during the period of egg 
laying. Now in Callinectes the endopodites are packed full of “ cement ” or tegumental 
glands; the exopodites contain fewer glands but an excess of cell disks or concretions 
(see 149, p. 108). In fact, Braun called attention to the presence of glands in these 
Brachyura over thirty years ago. 
If the secretion of the receptaculum seminis of the crabs is limited only to the uses 
of the sperm, as seems probable, we are inclined for the present to accept the older 
theory, namely, that eggs are glued to the hairs by a cement which is secreted by glands 
which lie at their base. 
Why the eggs of the Callinectes are not stuck together or why neighboring hairs do 
not more frequently adhere is not apparent, and can not be explained until we know 
more about the physical properties of the glue itself. The hairs of Callinectes are 
covered with a continuous sheet of glue, but are not often adherent. Possibly the eggs 
stick to them before they have a chance to become entangled. Each egg is tethered by 
a thin spun sheet of glue, which is continuous with a narrowband or sheet, in which the 
entire hair is embraced up to the tip or very close to it. 
As was pointed out by the writer in 1892 and as had already been demonstrated by 
Mayer in 1877, the crustacean egg does not possess a yolk-membrane. The ovarian 
ovum and the mature egg when it issues from the ovary, in crustaceans as well as in 
insects, is provided with a single membrane, the chorion, which is secreted by the “ovi- 
sac” or egg follicle. The great mass of the egg is made up of inert yolk; the protoplasm, 
which alone has formative power, is practically restricted to the center of the egg. When 
in the course of segmentation or later the protoplasm has reached the surface, a delicate 
membrane is secreted by the blastoderm. This often glues the egg fast to the chorion 
and gives much trouble to the embryologist. No doubt it was this membrane which 
ga/e rise to the mythical “ Dotterhaut, ” or vitelline membrane of Erdl, Rathke, and the 
older school of embryologists. 
A single membrane only, the chorion, is apparent in the eggs of Callinectes, but since 
the cord of attachment spreads out over its surface without any apparent break, the egg 
is probably covered with a thin layer of cement which has the same index of refraction 
as the chorion to which it is inseparably glued. 
Williamson endeavors to extend his ingenious theory of fixation by “spearing” and 
the liberation of the cement from the egg itself to the lobster and other Macrura. Thus 
he says that the secretion “is not a true cement” capable of forming an outer envelope, 
but an albuminous substance, and that “the weight of the egg tends to stretch out the 
ductile chorion into long thin stalks.” It is quite certain that the egg of the lobster, as 
in all the higher Crustacea, possesses a single membrane when it leaves the ovary, but 
the egg attached to the body has acquired a second and distinct membrane which is 
continuous with the stalk of attachment. The two are easily separable in picro-sulphuric 
acid; the second or outer layer is the “cement membrane” (fig. 5, pi. xliv). 
As we have already seen (p. 305) the eggs of the lobster are attached to the non- 
plumose hairs of the swimmerets as well as to the abdomen and to each other. Here at 
