This section is from the book "General Outline Of The Organization Of The Animal Kingdom, And Manual Of Comparative Anatomy", by Thomas Rymer Jones. Also available from Amazon: A General Outline of the Animal Kingdom and Manual of Comparative Anatomy.
In order to form the door in question, the Mygale first spins a web which exactly covers the mouth of the hole, but which is attached to the margin of the aperture by one point only of its circumference, this point, of course, forming the hinge. The Spider then proceeds to lay upon the web a thin layer of the soil collected in the neighbourhood of her dwelling, which she fastens with another layer of silk; layer after layer is thus laid on, until at length the door acquires sufficient strength and thickness: when perfected, the concealment afforded is complete; for as the outer layer of the lid is formed of earth precisely similar to that which surrounds the hole, the strictest search will scarcely reveal to the most practised eye the retreat so singularly defended.
Fig. 193. Spinning apparatus of the Spicier.
Fig. 194. Silk-secreting glands of the Spider.
(980). Another Spider (Ch-tho Durandii) constructs a dwelling equally artificial and ingenious - a kind of tent, in which it lives and rears its young. This tent is composed of several superposed sheets of the finest taffeta, and its contour presents seven or eight prominent angles, which are fixed to the surface of the ground by silken cords. The young Clotho at first lays down only two sheets thus secured, between which she hides herself; but, as she grows older, she continually lays down additional coverings, until the period when she begins to lay her eggs, at which time she constructs an apartment, soft, downy, and warm, specially devoted to their reception. The exterior sheet of the tent is purposely dirtied for the purpose of concealment; but, within, everything is beautifully clean and white. The most admirable part of the contrivance, however, is the perfect safety afforded to the young when the parent leaves her tent in search of food: some of the superposed sheets are fastened together at their edges; others are simply laid upon each other; and as the parent herself alone possesses the secret which enables her to raise those layers by which entrance is to be obtained, no other animal can find its way into her impenetrable abode.
Fig. 194a. Anatomy of Mygale: a, centralized ganglia of the nervous system; b, termination of the ganglionic cord; c, respiratory stigmata; d, anterior pulmoni-hranchial organ of the left side, displayed; e, posterior pulmonibranchial organ, partially covered by a large abdominal muscle (i); f, ovary; g, section of integument; h, spinnerets and anal aperture.
Fig. 194b. 1. Female of Hydrachne globulus, represented of the natural size just previous to ovipo-sit ion. 2. The same magnified, and seen from below, showing the mouth or beak furnished with two palpi, and the eight legs appended to four separate pairs of coxae; between the hinder pair may be seen the heart-shaped genital scale, and a little posterior to this a round orifice, which is the anus. 3. Newly-hatched larva of Hydrachne globulus. 4. Hinder part of an aquatic insect (Nepa cinered), to which numerous nymphae of Hydrachne indifferent stages of growth are attached. 5. One of these nymphs magnified, exhibiting the head-like sucker provided with a pair of palpi, immediately behind which are seen two of the epidermic cases of two of the old legs of the larva (the four others have fallen off), and posterior to these, five pairs of little sprouts, which are the rudiments of antennae and legs: the median circle indicates the position of the genital organs. 6. Represents the same nymph in its last stage of development, seen in profile: the integuments are supposed to be transparent, so as to show the young Hydrachne within, ready to escape. 7. Ventral surface of young Hydrachne, showing the arrangement of the coxae. 8. Secondary nymph making the transition from the second to the third phasis of the creature's existence: the perfect animal, ready for its escape, is represented encased in the integuments of the preceding, the epidermic sheaths of the limbs still remaining adherent to the exuvium.
(980a.) The development and mode of exuviation of some of the Acaridans offer several very curious and interesting phenomena. The Hydrachne, or Water-mites, for example, at their birth present themselves under the form represented in fig. 194b, 3, being at that time provided with only six locomotive limbs and a very remarkable proboscis*. These larvae at first swim at large in the water, but at length contrive to fix themselves to the body of some aquatic insect, in which position they pass into the state of nymphs (fig. 194b, 4); the hinder part of their bodies becomes remarkably elongated, and at length assumes the form of a pear, in which all resemblance to its former state is lost. Nevertheless, during this remarkable increase in size, the proboscis and the legs undergo but little alteration; for as soon as the body begins to elongate, the legs and the palpi are withdrawn from their original integument, and, retiring with the body into the pear-shaped sac formed by the distended skin, nothing is left behind but the exuviated sheaths of the old legs, which are then easily broken off by the slightest violence. A nymph, formed in the interior of its own skin, has replaced the larva; but it is a nymph which continues to nourish itself, and to increase in size, until it assumes the appearance shown at fig. 194b, 5, in which the rudiments of a new set of legs are clearly perceptible through the transparent envelope: the eyes of the contained animal are distinctly traceable, and may even be seen to abandon their former corneae, and to recede in the same proportion as the limbs from the old case, which at last, rending transversely into two portions, allows the new animal to escape, which immediately begins to swim vivaciously about, under a form closely resembling that of the parent. It has, however, still another moult to go through before it can be pronounced adult; for, after having lived some weeks in this third condition, and visibly increased in size, these immature individuals fix themselves to some water-plant, to which they hold firmly by means of their beak and claws, and, becoming motionless, again exuviate (fig. 194b, 8), and are ready to reproduce their kind.