GROWTH IN THE EGG.
The egg of a spider, like that of any other animal, is a cell which separates from the body of the female, and afterwards unites with one or more cells which have separated from the body of the male. This fertilization of the eggs probably takes place when they have reached their full size, and are about to be laid.
After the eggs are laid and hardened, it is very easy to watch their development. They grow just as well anywhere else as in the cocoon, and, in order to see through the shell, it is only necessary to cover the egg to be examined, with oil, alcohol, or any liquid that will wet it.
Fig. 63.
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.
Fig. 64.