Their number is considerable.  A patient and careful census gives me nearly six hundred.  And all this comes out of a purse no larger than a pea.  By what miracle is there room for such a family?  How do those thousands of legs manage to grow without straining themselves?

The egg-bag, as we learnt in Chapter II., is a short cylinder rounded at the bottom.  It is formed of compact white satin, an insuperable barrier.  It opens into a round orifice wherein is bedded a lid of the same material, through which the feeble beasties would be incapable of passing.  It is not a porous felt, but a fabric as tough as that of the sack.  Then by what mechanism is the delivery effected?

Observe that the disk of the lid doubles back into a short fold, which edges into the orifice of the bag.  In the same way, the lid of a saucepan fits the mouth by means of a projecting rim, with this difference, that the rim is not attached to the saucepan, whereas, in the Epeira’s work, it is soldered to the bag or nest.  Well, at the time of the hatching, this disk becomes unstuck, lifts and allows the new-born Spiders to pass through.

If the rim were movable and simply inserted, if, moreover, the birth of all the family took place at the same time, we might think that the door is forced open by the living wave of inmates, who would set their backs to it with a common effort.  We should find an approximate image in the case of the saucepan, whose lid is raised by the boiling of its contents.  But the fabric of the cover is one with the fabric of the bag, the two are closely welded; besides, the hatching is effected in small batches, incapable of the least exertion.  There must, therefore, be a spontaneous bursting, or dehiscence, independent of the assistance of the youngsters and similar to that of the seed-pods of plants.

When fully ripened, the dry fruit of the snap-dragon opens three windows; that of the pimpernel splits into two rounded halves, something like those of the outer case of a fob-watch; the fruit of the carnation partly unseals its valves and opens at the top into a star-shaped hatch.  Each seed-casket has its own system of locks, which are made to work smoothly by the mere kiss of the sun.

Well, that other dry fruit, the Banded Epeira’s germ-box, likewise possesses its bursting-gear.  As long as the eggs remain unhatched, the door, solidly fixed in its frame, holds good; as soon as the little ones swarm and want to get out, it opens of itself.

Come June and July, beloved of the Cicadae, no less beloved of the young Spiders who are anxious to be off.  It were difficult indeed for them to work their way through the thick shell of the balloon.  For the second time, a spontaneous dehiscence seems called for.  Where will it be effected?

The idea occurs off-hand that it will take place along the edges of the top cover.  Remember the details given in an earlier chapter.  The neck of the balloon ends in a wide crater, which is closed by a ceiling dug out cup-wise.  The material is as stout in this part as in any other; but, as the lid was the finishing touch to the work, we expect to find an incomplete soldering, which would allow it to be unfastened.