The Structure and Habits of SpidersEmerton, J. H. (James Henry)
Science
The Structure and Habits of Spiders
Emerton, J. H. (James Henry)
Spiders
Just after it is laid, the egg looks like Fig. 63, _a_; or, if the egg
is more opaque, only the ends of the lobes can be seen like irregular
lumps. The first sign of growth is the division into two, Fig. 63, _b_.
These divide into four, into eight, and so on, Fig. 63, _c_, _d_. At
first the divisions are all alike; but at length they divide into two
kinds,—small ones, with a dark spot in the middle, which cover the
outside of the egg; and larger ones that occupy the inside. Fig. 63,
_e_, shows an egg at this stage, where the large inner cells show
through the layer of outer ones. Fig. 63, _f_, is a section of the same
egg. The stages shown in _b_ and _c_ are seldom clearly seen, because
the divisions are crowded together and too opaque; but _d_ and _e_
can be watched in any common spider’s eggs. The rate of growth varies
according to circumstances. Some eggs laid in autumn develop slowly all
winter, while others laid in summer are ready to hatch in a fortnight.
In the eggs of the long-legged cellar spider, laid in June, in about
four or five days the young spider becomes lengthened out into a sort
of barrel shape; and six whitish rings run half way round it, on each
of which appears soon after a pair of little knobs, one each side, Fig.
64, _a_. These are the six segments of the thorax, and the six pairs of
limbs; and their gradual growth is shown in Fig. 64, _b_, _c_, _d_. In
_a_ there is no sign of a head or abdomen, except the more opaque ends
of the embryo; but shortly after there appears an opaque knob at one
end, Fig. 64, _b_, under which is a pair of little knobs, such as
appeared at first on the thoracic segments; then appear two pairs, then
three, and so on, till there are six pairs, which mark the six segments
of the abdomen. Up to this time, the embryo has been rolled up with the
under side outward; but now it begins to turn, and in a day or two has
its back outward, Fig. 64, _c_. The constriction between the thorax and
abdomen begins about this time; and in a few days more the spider is
ready to hatch, Fig. 64, _d_.
[Illustration: Fig. 64.]
YOUNG SPIDERS.
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