Arachnid

“ Another very disgusting arachnid liable to attack man is the Galeodes araneoides. This large spider-like creature, two inches in length, commonly attacks camels and has an extremely venomous bite. One or more species of the dung-beetle mites (Gamasidæ) have also been known to fasten themselves on man. ”

“ There is no doubt, from a consideration of the facts of structure, that the aquatic water-breathing Arachnids, represented in the past by the Eurypterines and to-day by the sole survivor Limulus, have preceded the terrestrial air-breathing forms of that group. Hence we see at once that the better-known Arachnida form a series, leading from Limulus-like aquatic creatures through scorpions, spiders and harvest-men, to the degenerate Acari or mites. ”

“ ARACHNIDA—INTRODUCTION The Arachnida, together with the Crustacea, Insecta, Myriapoda, and Peripatus, make up the great phylum Arthropoda, a phylum which, from the point of view of numbers of species and of individuals, is the dominant one on this planet, and from the point of view of intelligence and power of co-operating in the formation of social communities is surpassed but by the Vertebrata. The Arachnida form a more diverse class than the Insecta ”

“ Another disagreeable arachnid is the little harvest bug (Leptus autumnalis) , which not only excites irritation during its crawling motion on the human skin, but even succeeds in burying itself near the hairs. The irritation thus produced is almost unbearable. This mite attacks various animals, especially dogs and cats. I myself once suffered severely from this species in consequence of fondling a young wild rabbit which, as I afterwards discovered, was much infested. When the parasites had reached my left arm-pit they occasioned extreme torture. ”

“ This concentration and obliteration of somites, often accompanied by dislocation of important segmental structures (such as appendages and nerve-ganglia) , may lead to highly developed specialization (individuation, H. Spencer) , as in the Araneae and Opiliones, and, on the other hand, may terminate in simplification and degeneration, as in the Acari.}
The most important general change which has affected the structure of the nomomeristic Arachnida in the course of their historic development is the transition from an aquatic to a terrestrial life. ”

“ The Acarina or Mites are remarkable not so much for the number of their species, which is very considerable, as for the vast multitude of individuals of the Order, which is far in excess of that of any other Arachnid group. This fact is correlated with their minute size. Very few Mites exceed half an inch in length, while very many are microscopic creatures, often measuring less than the hundredth of an inch. ”

“ In the numerous degenerate forms simplification occurs by obliteration of the demarcations of somites and the fusion of body-regions, together with a gradual suppression of the lamelliferous respiratory organs and the substitution for them of tracheae, which, in their turn, in the smaller and most reduced members of the group, may also disappear. The Eu-arachnida are divided into two grades with reference to the condition of the respiratory organs as adapted to aquatic or terrestrial life. ”

“ When it is admitted—as seems to be reasonable—that the primitive Arachnida would, like the primitive Crustacea, be anomomeristic and anomotagmic, we shall not demand of claimants for the rank of primitive Arachnids agreement with Limulus and Scorpio in respect of the exact number of their somites and the exact grouping of those somites; and when we see how diverse are the modifications of the branches of the appendages both in Arachnida and in other classes of Arthropoda (q.v.) ”

“ The Arachnida are so varied in structure that it is not easy to give characteristics common to them all, and to any general statement there are bound to be exceptions, but for practical purposes it may be said that while an insect, when mature, has only six legs, and a pair of feelers or antennae of quite different structure, Arachnids have normally eight legs, and their feeling organs are not antennae but leg-like “pedipalps.” ”

“ The inference is obvious, that the marine arachnids, the ostracoderms, and the fishes, represent three successive stages in the evolution of the animal kingdom, just as in the later periods the fishes, amphibia and mammals represent successive stages in the evolution of the vertebrates. If this inference is correct, then the whole creative period in the evolution of the vertebrate stock should become an open book, because the materials, both living and fossil, with which one can unravel the evolution of the arachnids, are apparently abundant and accessible. ”

“ Dividing the vertebrate animals—as Linnæus had already divided them—into mammals, birds, reptiles, and fishes, he divided the invertebrates into molluscs, insects, worms, echinoderms, and polyps. In 1799 he separated the crustacea from the insects, with which they had been classed hitherto; in 1800 he established the arachnids as a class distinct from the insects ”

“ Little apparatus is necessary in the collection of spiders and other Arachnids. The essentials are vials containing alcohol, an insect net, a sieve, and forceps. Narrow vials without necks are best for collecting purposes, as the corks can be more quickly inserted. They should be of different sizes, from 1 dram to 4 or 6 drams, and the alcohol used should be at least 50 per cent strong and in some cases it is advisable to use it at a strength of 70 or 80 per cent. The net may be of the same construction as that used to collect insects and is used in the same way. ”

“ The Arachnida differ from insects, in having eight or more legs, more than two eyes, no wings, and no head; the Spiders have four pairs of legs, and six, eight, or more, simple eyes, which appear as minute spots on the upper part of the thorax. Spiders nearly all live by preying upon small insects, which they catch in several ways, but by far the most general mode is by constructing a web or net to entangle them ”

“ There are two main lateral trunks extending nearly the whole length of the body, and giving off numerous ramifications, the most important of which are in the cephalothorax, and supply the muscles of the chelicerae and of the other appendages.
The generative glands do not essentially differ from the usual Arachnid type, though the paired ovaries do not fuse to form a ring. There are no external organs, and the sexes can only be distinguished by secondary characteristics, such as the “flagellum” already mentioned. ”

“ PANTOPODA.—Nomomeristic Arachnids, in which the somites corresponding to mesosoma and metasoma have entirely aborted. The seventh, and sometimes the eighth, leg-bearing somite is present and has its leg-like appendages fully developed. Monomeniscous eyes with a double (really triple) cell-layer formed by invagination, as in the Eu-arachnida, are present The Pantopoda stand in the same relation to Limulus and Scorpio that Cyamus holds to the thoracostracous Crustacea. ”

“ The first segment of the mesosoma of Scorpio and Limulus thus remains the first segment, and can be identified as such throughout the Eu-arachnida, carrying as it always does the genital apertures. But it is necessary to remember, in the light of recent discoveries, that the sixth prosomatic pair of appendages is carried on the seventh somite of the whole series, there being two prosthomeres or somites in front of the mouth, the first carrying the eyes, the second the chelicerae ”

“ After Mégnin.
The ectoparasitic arachnidans comprise a great variety of mites and ticks (Acaridæ and Ixodidæ) more or less proper to man, and also a number of creatures which, though hardly to be reckoned as human parasites, are apt to transfer themselves from animals to man. Little more than an enumeration of the forms is possible here. The Common Scab or Itch insect (Sarcoptes scabiei) forms the type of a great variety of arachnids, generally spoken of as different species according to the host they dwell upon. ”

“ ARACHNIDA, the zoological name given in 1815 by Lamarck (Gr. ἁράχνη, a spider) to a class which he instituted for the reception of the spiders, scorpions and mites, previously classified by Linnaeus in the order Aptera of his great group Insecta. Lamarck at the same time founded the class Crustacea for the lobsters, crabs and water-fleas, also until then included in the order Aptera of Linnaeus. Lamarck included the Thysanura and the Myriapoda in his class Arachnida. The Insecta of Linnaeus was a group exactly equivalent to the Arthropoda founded a hundred years later by Siebold and Stannius. ”

“ From activity in seizing, tearing, and devouring their food, and from their pugnacity, crabs are interesting inmates of the aquarium. They also moult, or cast off their shells; not at regular seasons, but when the demand for more room requires it.
Class II.—Arachnida are closely related to the crustaceans, having, like them, the body divided into two sections—cephalo-thorax and abdomen. To the former are attached four pairs of legs, but the abdomen has no appendages for locomotion. There are about 5,000 species, produced from eggs, and undergoing no metamorphoses in their development. ”

“ It may in this connection be observed that some authors derive the book-lungs or book-leaf tracheæ of Arachnida from the gills of Limulus; hence if those of Arachnida arose from quite different and more specialized organs than dermal glands, it is not impossible that the tracheæ of Peripatus, Myriopods, and insects arose de novo, and then we need not look for any primitive structures in worms from which they arose. ”

“ Others are found in different parts of the globe, and twenty-four species have been described. Several new American Ixodes have been noticed lately by Mr. Packard on the stag, the monax marmot, the Lepus palustris, &c. These arachnida live at first in freedom in the bushes, but after fecundation the female attacks the first mammal which she finds in her way, and establishes herself upon it; dogs become infested with it by running in and out among the brushwood. ”

“ The fact that the single pair of prae-oral appendages of trilobites, known only as yet in one genus, is in that particular case a pair of uni-ramose antennae—does not render the association of trilobites and Arachnids improbable. Although the prae-oral pair of appendages in the higher Arachnida is usually chelate, it is not always so; in spiders it is not so; nor in many Acari. ”

“ HARVEST-BUG, a name erroneously applied to the hexapod larval condition of a mite, not one of the Insecta, but belonging to the division Acaridea of the class Arachnida. It is very small, of a brick-red colour, and swarms both among wild vegetation and cultivated plants, especially near the sea, attaching itself, however, on the first opportunity to the bodies of human beings, hares, dogs, cats, and other mammals, and even insects. ”

“ In the larger and more complex Arachnida the number of segments is fixed and constant, and though possibly no adult member of the group, owing to the suppression of one or more segments during the ontogeny, ever shows the full number at any one time, the body can be analysed into twenty-one segments. ”

“ But most important of the evidences presented by the trilobites of affinity with Limulus, and therefore with the Arachnida, is the tendency less marked in some, strongly carried out in others, to form a pygidial or telsonic shield—a fusion of the posterior somites of the body, which is precisely identical in character with the metasomatic carapace of Limulus. ”

“ Remarks on the Araneae.—The Spiders are the most numerous and diversified group of the Arachnida; about 2000 species are known. No noteworthy fossil spiders are known; the best-preserved are in amber of Oligocene age. Protolycosa and Arthrolycosa occur in the Carboniferous. Morphologically, the spiders are remarkable for the concentration and specialization of their structure, which is accompanied with high physiological efficiency. ”

“ If any one is so ill advised as to take one of these Arachnides into his confidence, he is sure to smart for it. Has he complained of a common friend?—the grim confidant rasps the little abrasion till it becomes a gangrened sore, and never lets it alone till it has lost all power of healing. ”

“ But the modern land arachnids are descendants of a large group of very ancient marine arachnids, the trilobites and merostomata, or giant sea-scorpions, which flourished in the early Cambrian and Ordovician periods, long before any vertebrates were known to exist. ”

“ He suggests that the arachnids also form an ancient type, and that the common origin of the merostomes and the arachnids must be sought for far down in the pedigree of the arthropods. "The agreement between scorpions and eurypterids would then be derived from causes quite independent of close relationship, and perhaps from a convergence in some branches of the two stems which are formed by the merostomes and the arachnids." ”

“ It has been considered by them as proving that Limulus, in spite of all its special agreements with Scorpio (which, however, have scarcely been appreciated by the writers in question) , really belongs to the Crustacean line of descent, whilst Scorpio, by possessing Malpighian tubes, is declared to be unmistakably tied together with the other Arachnida to the tracheate Arthropods, the Hexapods, Diplopods, and Chilopods, which all possess Malpighian tubes. ”

“ Toiling with what appeared to be a furious haste were hundreds of the arachnida at respinning damaged traps torn and (illegible text) ed in the recent passage of the night, revolting-looking creatures they were with bodies as large as a silver dollar and a span of the legs as big as a daddy-long-legs but with much more powerful limbs. ”

“ Their presence in society reminds one of the winter whose ‘Breath was a chain which without a sound, The earth and the air and the water bound.’ Where they are, freedom flags and gaiety declines; and only the most robust of those moral pachyderms who oppose their thick insensitiveness to all outside influences whatsoever, can withstand the lethal effect of the Arachnides. Their small pale eyes wither; their pinched lips paralyse; their very smiles are the fracture of a crystal more than the visible sign of a living, friendly heart; and they are the veritable ‘freezing mixtures’ of life. ”