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CHAPTER XIX.

Functions and Instincts. Arachnidan, Pseudarachnidan, and Acaridan Condylopes.

HAVING wandered long enough, perhaps too long, in a wide and mazy field, but fertile every where in proofs of the Power, Wisdom, and goodness of the Creator, it is time to return to the high road from which we diverged.

The Class of animals which led me into this digression were the Myriapods, concerning which I observed, when I commenced my account of them, that on quitting the Crustaceans, the way seemed to branch off from the long-tailed Decapods by them, and from the short-tailed ones by the Arachnidans. We are now then to give a history of the latter Class.

Latreille, in which he has been followed by most modern Arachnologists, in his work in aid of Cuvier's last edition of the Règne Animal,' divides his Arachnidans into two Orders, Pul monaries, or those that breathe by gills, and Trachearies, or those that breathe by spiracles in connexion with trachea. In his latest work, which he did not live to finish, he added a third Order, including some parasites, infesting marine animals, such as the whale-louse. These, from their having no apparent respiratory apparatus, he named, Aporobranchians.

As the pulmonary Arachnidans of Latreille differ from the Trachearies, &c., not only in having their body divided into two sections, but likewise both in their respiratory organs and those of circulation, I have always regarded them as forming a distinct Class.*

The following characters distinguish this Class;

BODY covered by a coriaceous or horny integument, divided into two segments. Head and trunk confluent so as to forma single segment, denominated the Cephalothorax. Eyes, 6—8.

1 Les Crustacés, les Arachnides, et les Insectes.

2 Cours D'Entomologie.

3 Nymphon grossipes.

4 Introd. to Ent. iii. 19, 24.

Legs, 8. Spinal chord, knotty. A heart and vessels for circulation. Respiration by gills. Sexual organs, double. This Class consists of two Orders.

1. Araneidans. Integument coriaceous. Mandibles, also called cheliceres, consisting of a single joint, armed with a claw, perforated near the apex for the transmission of venom, and, when unemployed, folding upon the end of the mandible. Gills, 2-4. Abdomen united to the trunk by a foot-stalk. Anus furnished with 4-6 spinning organs. 2. Pedipalps. Integument horny. Feelers extended before the head, armed with a forceps or didactyle claw. Abdomen sessile. Gills, 4-8.

1. Araneidans, or spiders.

No animals fall more universally under observation than the spiders; we see them everywhere, fabricating their snares or lying in wait for their prey, in our houses, in the fields, on the trees, shrubs, flowers, grass, and in the earth; and, if we watch their proceedings, we may sometimes see them, without the aid of wings, ascend into the air, where, carried by their web as by an air-balloon, they can elevate themselves to a great height. The webs they spin and weave are also equally dispersed; they often fill the air, so as to be troublesome to us, and cover the earth. M. Mendo Trigozo relates, that at Lisbon, on the 6th of November, 1811, the Tagus was covered, for more than half an hour, by these webs, and that innumerable spiders accompanied them, which swam on the surface of the water. I have, in another place, given an account of the instruments by which they weave them; and shall now say a few words upon those by which their Creator has enabled them to produce the material of which they are formed.

At the posterior extremity of the abdomen, formed usually by a prominence, is the anus, immediately below which, planted in a roundish depressed space, are four or six jointed teat-like organs, of a rather conical or cylindrical shape. The exterior pair is the longest, consisting of three joints; but these have no orifices at their extremity for the transmission of threads; the other four consist each of two joints, and are pierced at their extremity with innumerable little orifices, in some species amounting to a thousand from each, from which their web

1 Manipalps would be a more proper term, as the feelers are used for prehension, not for walking. 3 See above, p. 286.

2 Latr. Cours. D'Ent. i. 497.

4 Mammule, Introd. to Ent. iii. 391.

issues at their will, or bristled with an army of infinitely minute biarticulate spinnerets,1 each furnishing a thread at their extremity. These teats are connected with internal reservoirs, which yield the fluid matter forming the thread or web. These reservoirs in some species consist of four, in others of six ves sels folded several times, and communicating with other vessels in which the material that forms their web is first elaborated."

Such are the organs which furnish the material of those wonderful and diversified toils which the spiders weave to entrap the animals that form their food.

The threads, after they issue from these organs, are united, or kept separate, according to the will or wants of the animal; and it is stated, that from them certain spiders can spin three kinds of silk. Their ordinary thread is so fine, that it would require twenty-four united to equal the thickness of that of the silkworm. These threads, fine as they are, will bear, without breaking, a weight sextuple that of the spider that spins them. They employ their web, generally, for three different purposes; in the construction of their snares, of their own habitations, and of a cocoon to contain their eggs.

Spiders were divided by the older Arachnologists, after Lister, into families, according to the mode in which they entrap or seize their prey. More modern writers on the subject have taken their respiratory organs as regulating the primary division of the Order: upon this principle, the spiders are formed into two tribes-those that have two pairs of gills; and those that have only one pair. M. Walckenaer, who has studied the Order more than any man in Europe, has not only divided the above two tribes into genera, &c., from characters taken from their form and organization; but has also considered them with respect to their habits, and under this head divides them into four sections:

1. Hunters, wandering incessantly to entrap their prey. 2. Vagrants, watching their prey, concealed or inclosed in a nest, but often running with agility.

3 Sedentaries, forming a web in which they remain immovable.

4. Swimmers, swimming in the water to catch their prey, and there forming a web.

1 Fusi, Introd. to Ent. iii. 392.

3 Blackwall, in Linn. Trans, xvi. 479.

2 Latr. Cours D'Ent, i 496. 4 L. Du Four.

5 Tetrapneumones. Latr. Theraphosa, &c., Walck.

6 Dipneumones. Latr. Aranea. Walck. excluding Dysdera.

Latreille.

To the first tribe, those, namely, with four gills, some spiders belong, the instincts of which are very remarkable. One of the largest, and most celebrated, is the bird-spider.1 It forms the tube which it inhabits of a white silk like muslin, which it fixes amongst leaves, and in any cavities, and there watches its prey; it is accused by some of destroying even birds, whènce its name, especially the humming-bird: but this rests upon questionable authority; and writers are not agreed as to its general habits. Probably several species are confounded under the same name. I shall not therefore enlarge further on its history; I mention it merely as the largest spider known.

The proceedings of those called the trap-door spiders are better authenticated, as those of the mason-spider by the Abbé Sauvages, and those of another species very recently, in the annals of the French Entomological Society, by M. V. Audoin, one of the most eminent of modern entomologists, under the name of the pioneer; of his interesting memoir, I shall here give a brief abstract.

Some species of spiders, M. Audoin remarks, are gifted with a particular talent for building: they hollow out dens; they bore galleries; they elevate vaults; they build, as it were, subterranean bridges: they construct also entrances to their habitations, and adapt doors to them, which want nothing but bolts, for without any exaggeration, they work upon a hinge, and are fitted to a frame."

The interior of these habitations, he continues, is not less remarkable for the extreme neatness which reigns there; whatever be the humidity of the soil in which they are constructed, water never penetrates them; the walls are nicely covered with a tapestry of silk, having usually the lustre of satin, and almost always of a dazzling whiteness. He mentions only four species of the genus as at present known. One which was found in the Island of Naxos; another in Jamaica; a third in Montpellier; and a fourth, that which is the subject of his Memoir, in Corsica; to which I may add a fifth species, found frequently by Mr. Bennet, in different parts of New South Wales.10

The habitations of the species in question, are found in an

1 Mygale avicularia.

4 Ct. Sauvagesii.

2

Trochilus.
5 Ct. fodiens.

3 Cleniza.

6 The French word is feyure, which I cannot find in the dictionaries, but it means, the eircular frame of the mouth of the tube which receives the door.

[blocks in formation]

10 Wanderings in N. S. Wales, &c. i. 328.

9 Ct. comentaria.

argillaceous kind of red earth, in which they bore tubes about three inches in depth, and ten lines in width. The walls of these tubes are not left just as they are bored, but they are covered with a kind of mortar, sufficiently solid to be easily separated from the mass that surrounds it. If the tube is divided longitudinally, besides this rough cast, it appears to be covered with a coat of fine mortar, which is as smooth and regular as if a trowel had been passed over it; this coat is very thin, and soft to the touch; but before this adroit workman lays it, she covers the coarser earthy plaster-work with some coarse web, upon which she glues her silken tapestry.

All this shows that she was directed in her work by a Wise Master; but the door that closes her apartment is still more remarkable in its structure. If her well was always left open, she would be subject to the intrusion of guests that would not, at all times, be welcome or safe; Providence, therefore, has instructed her to fabricate a very secure trap-door, which closes the mouth of it. To judge of this door by its outward appearance, we should think it was formed of a mass of earth coarsely worked, and covered internally by a solid web; which would appear sufficiently wonderful for an animal that seems to have no special organ for constructing it: but if it is divided vertically, it will be found a much more complicated fabric than its outward aspect indicates, for it is formed of more than thirty alternate layers of earth and web, emboxed, as it were, in each other, like a set of weights for small scales.

If these layers of web are examined, it will be seen that they all terminate in the hinge, so that the greater the volume of the door, the more powerful is the hinge. The frame in which the tube terminates above, and to which the door is adapted, is thick, and its thickness arises from the number of layers of which it consists, and which seem to correspond with those of the door; hence, the formation of the door, the hinge, and the frame, seem to be a simultaneous operation; except that in fabricating the first, the animal has to knead the earth, as well as to spin the layers of web. By this admirable arrangement, these parts always correspond with each other, and the strength of the hinge, and the thickness of the frame, will always be proportioned to the weight of the door.

The more carefully we study the arrangement of these parts, the more perfect does the work appear. If we examine the circular margin of the door, we shall find that it slopes inwards, so that it is not a transverse section of a cylinder, but of a cone, and on the other side, that the frame slopes outwards, so that the door exactly applies to it. By this structure, when the door

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