1902 Encyclopedia > Arachnida > Arachnida - Order IV: Solpugidea - Internal Structure

Arachnida
(Part 13)



(13) ARACHNIDA - ORDER IV: SOLPUGIDEA - INTERNAL STRUCTURE

INTERNAL STRUCTURE. - The Muscular System of Solpugids appears to be very similar to that of other Arachnids; it has been fully displayed by Dr M. Kittary in the work quoted in note, of the present page.

The Respiratory System is tracheal and complicated. Five (according to Dr Kittary) openings at the hinder margins of the second, third, and fourth sub-abdominal articulations, lead to the abdominal tracheae; these consist of three longitudinal parallel tubes, into the outer one of which the short branches from the external openings lead and with these are connected various other branches supplying air to the different parts of the body. The abdominal traceae also lead into those of the cephalo-thorax, which have their outer openings (two in umber) behind the basal joints of the second pair of legs. The thoracic tracheae send branches into the legs, palpi, and falces.

There is probably some variation in different species in the detail of their respiratory organs. Galeodes Araneoides, for instance, does not appear to have the fifth outward opening in the abdomen (fig. 15).

The Circulatory System consists of an elongated dorsal vessel or heart, running from the middle of the cephalo-thorax backwards through the connection between the thorax and abdomen, but does not reach the hinder extremity of the latter. The thoracic portion is of an oval form, but it contracts in passing into the abdomen, enlarging again gradually as it runs backwards. Dr Kittary does not appear to have traced the various vessels which, no doubt, exist to convey the vital fluid from the heart to the different parts of the body.

The Organs of Digestion consist of an elongated stomach in the cephalo-thorax, with lateral caeca; this stomach is continued backwards into the abdomen in the form of a long single intestinal canal, leading into a cloaca at its posterior extremity. A kind of branching network of minute vessels secrete urine, and convey it from the whole abdominal mass by several main branches into the hinder part of the intestinal canal. Beneath the stomach is an organ described as probably the liver, and another answering to the pancreas.

The Nervous System is not particularly complicated, but bears great resemblance to that of other Arachnids, especially of the Araneidea. It consists of one large principal ganglion, or united pair of ganglia, from which branch nerves are sent off in all directions to the different parts and extremities of the body; that which runs to the hinder extremity of the abdomen has an enlargement or kind of ganglion in its course.

The Organs of Generation are highly developed in the female, consisting of ovaries, and an oviduct leading to the external orifice. The male organs do not appear to be known. The Solpugidea are probably oviparous.

The order Solpugidea comprises a single family, Galeodides, divided into five genera, characterized principally according to the number of the subdivisions of the tarsal joints of the second, third, and fourth pairs of legs; - 1. Rhax (Hermann), the tarsi all one-jointed. 2. Aellopus (Koch), tarsi two-jointed; those of the hinder pair destitute of claws (Koch). 3. Galeodea (Olivier), tarsi of the second and third pairs two-jointed, and of the fourth pair three-jointed. 4. Solpuga, tarsi of the second and third pairs four-jointed, and f the fourth pair seven- jointed. 5. Gluvia (Koch), all the tarsi undivided, i.e. consisting of a single long thin joint.

Fifty-two species (of all the genera) have been described. See a recent paper, List of the Species of Galeodides, by A.G. Butler; also the older work of Koch, Die Arachniden. All the species, though varying considerably in size, are remarkably similar in general form and appearance, and nearly all are of sombre colouring.





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