1902 Encyclopedia > Arachnida > Arachnida - Order IV: Solpugidea - Introduction; External Characters

Arachnida
(Part 12)



(12) ARACHNIDA - ORDER IV: SOLPUGIDEA - INTRODUCTION; EXTERNAL CHARACTERS

Order IV. - SOLPUGIDEA.

This order constitutes a small but very distinct and remarkable group of tropical and semi-tropical Arachnids. At first sight they remind us a good deal of the true spiders (Araneidea), but their position, when we examine their structure details, seems to be more naturally assigned between the Phalangidea and the next order (Scorpionidea) (figs. 14, 15).

Galeodes araneoides image

Fig. 14 -- Galeodes araneoides, Pallas. a, a, falces; b, eyes; c, head; d,d, thorax; f, abdomen; g, g, palpi; h, h, palpiform legs; k, digital joint (capsule); o, o, shear-like points of falx; r, anus.


Galeodes araneoides image

Fig. 15 -- Under side of Galeodes araneoides, with legs and palpi truncated. a, a, maxillae; e...e, basal leg joints; e* e* first joints of first pair of legs; f, labium; h, h, fish-tail appendages; t, external orifice of sexual organs; k, tongue; m, m, palpi; o, o, respiratory organs at base of second pair of legs; p...p, orifices leading to trachae at fore-margins of second and third segments of abdomen; r, anus; t, t, fixed upper fangs or claws of falces; u, u, movable lower ditto.ß


EXTERNAL CHARACTERS. - The body is elongated and clothed with hairs; it is divided, as in other Arachnids, into two main portions (cephalo-thorax and abdomen), but each of these portions is composed of several segments or articulations. The caput forms the first segment of the cephalo-thorax; and this is followed by three others closely united to each other, and of a somewhat quadrangular form. Close behind each coxal joint of the legs of the second pair is a small transverse slit or stigma leading to tracheae.

The eyes are two in number, and seated on a tuberculiform eminence on the fore part of the caput; this eminence is furnished with two long slender spines, placed in a transverse line between the eyes, and projecting forwards.

The legs, articulated by a fixed joint to the lower surface of the thoracic segments, are long and strong, furnished with hairs (some of which are remarkably long), bristles, and spines, varying in length and strength. The legs of the first pair are palpiform and not used in running, probably having the sole office of feelers. The number of joints of those of the first and second pairs is seven, while those of the third and fourth pairs have eight, an extra joint being inserted between the basal and next adjoining joints; the tarsi of the first pair are simple, or undivided, and terminate with two small curved claws, while those of the other three pairs are often divided into two, three, or more articulations, besides a small terminal or heel joint, from which spring two long curved finger-like claws, each ending with a curved (apparently movable) nail or talon. The number, however, of the tarsal joints appears to differ in some species from others, and even in the different legs of the same species. The legs of the second, third, and fourth pairs belong to the three thoracic segments respectively, while those of the first pair are closely united (and even soldered) by their basal joints to the basal joints of the palpi beneath the caput, thus furnishing fan additional reason for supposing them to be more of a palpal than of a crural nature; between the bases of the first pair is a small triangular piece (with its apex directed forwards), unnoticed by authors hitherto (?) and which may be regarded as a rudimentary sternal lip (labium); on the under sides of the three basal joints of each of the fourth pair of legs is a longitudinal row of five curious scale-like or lamelliform appendages, of a subtrinagular or somewhat fish-tail form, each articulated to a separate foot-stalk, which is again articulated to the surface of the leg joint; beginning from the basal joint the form of the last two of these appendages differs a little from that of the rest. that these remarkable portions of structure have some special office is scarcely to be doubted, but as yet their part in the animal economy has not even been conjectured. They appear to differ slightly in structure in different genera.





Articulated immediately below the fore-margin of the caput are two enormous, massive falces, each consisting of a single joint, and ending with a didactyle claw or pair of toothed jaws, the upper fixed, the lower movable, and articulated horizontally with a vertical movement, closing upon each other like scissors or shears; these falces are projected in a line almost parallel with the caput, and are generally equal in length to the whole of the cephalo-thorax. From the fore part of the upper side of each of the falces are often seen one or two curious elongate styliform appendages varying in size and form; their use, if any, which may be doubted, is unknown; they are probably distinctive of sex, and appear to be characteristic of species. Underneath the caput, and forming the basil joints of two long strong five-jointed palpi, are the maxillae; these are strong, cylindrical, and have a more or less strong blunt-pointed apophysis at the extremity on the inner side. Like similar parts in other Arachnids, these maxillae in conjunction with the affixed basal joints of the first pair of legs, form the lower boundaries of the mouth, the labium (mentioned above) being apparently too rudimentary to subserve any practical purpose. The palpi are furnished with hairs, spines, and bristles similar to the legs, and the last (digital) joint consists of a kind of capsule containing a peculiar organ, said to be protruded only when the animal is in a state of irritation, the use of which does not appear to be known; doubtless it has some special function beyond that of a mere palpus, and the analogy of the use of the palpi in the males of the Araneidea would lead us to suspect a similar use in the present instance, i.e. as connected in some way with the process of generation. Between and within the maxillae is a portion of the mouth organs, composed of several parts of a peculiar shape, and furnished with two slender feather like appendages; this is called by Walckenaer the lip (levre); but its place and office is undoubtedly more that of the tongue (languette), though probably in the rudimentary state of the true labium it partly performs the duty of a sternal lip. Duges and M. Edwards in Cuvier's Regne Animal (Arachnides, p. 83), speak of the "labre," but it is evident from their description that a portion of the languette is alluded to, not the part mentioned above as representing the labium. The abdomen is oblong, oval, or somewhat elliptic in its form, about equally convex above and below, and composed of nine or ten articulations, which decrease in breadth from the fore to the hinder extremity; it is closely united to the cephalo-thorax throughout its entire breadth. The external orifice leading to the organs of generation is situated at the posterior margin of the first articulation, and besides the two stigmata before alluded to, behind the basal joints of the second pair of legs, there are two other stigmatic openings at the hinder margin of each of the second and third articulations of the abdomen; these stigmata are protected by a kind of comb-like fringe, and the anal orifice consists of a long vertical slit situated at the extremity of the terminal articulation.





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