The following points have been made out in the anatomy of Thelyphonus.[[250]]
The alimentary canal commences after the mouth with a pharynx which, though not dilated, is furnished with sucking muscles. It then narrows into an oesophagus which passes through the nerve-mass, and afterwards dilates to form the mid-gut, which immediately gives off two large lateral diverticula which extend backwards, each having five lobes. There are also two median diverticula which proceed from the ventral surface and pass through the endosternite. The abdominal portion of the canal is entirely concealed by the great “liver” mass which communicates with it by four paired ducts in the anterior part of the abdomen. Behind the fourth abdominal segment the gut is narrow till it expands in the seventh segment into an hour-glass-shaped stercoral pocket which, according to Laurie, is a portion of the mesenteron.
The excretory organs are the Malpighian tubes and the coxal glands. The former are generally described as entering the anterior portion of the stercoral pocket, but according to Laurie they pass along its ventral surface, attached to it by connective tissue, and really enter at the posterior end. The coxal glands are well developed, and lie beneath the endosternite, opening near the first coxae.
The nervous system is much concentrated and of the usual Arachnid type. The median abdominal nerve has a ganglion towards its extremity, supplying, according to Bernard,[[251]] the muscles which move the tail. The heart is extremely long, and varies little in width. It has nine pairs of ostia[[252]]—two in the thorax and seven in the abdomen. The generative glands are paired, and in the male there are large seminal vesicles. In the most ventral portion of the abdominal cavity lies a remarkable asymmetrically-situated gland, the “stink-gland.” It consists of a number of secretory tubules communicating with two elongated sacs, one of which lies beneath the nerve-cord, and therefore medially, while the other lies far to the left. Their ducts proceed to the anus or its vicinity.
The caudal organs, or white spots which, as already mentioned, are usually found on the last of the three post-abdominal segments of Thelyphonus, are of doubtful function. They have been variously explained as the stink-gland orifices, and as organs sensitive to light (“ommatoids”). Laurie[[253]] was unable to find any pore in this region, nor was there any of the pigment so characteristic of organs of sight. The histological structure indicated a sense-organ rather than a gland, but the use of these organs is entirely conjectural.
Classification.—The order Pedipalpi is divided into three families—Thelyphonidae, Schizonotidae and Tarantulidae. The first two are considered by some authors to form a sub-order, Uropygi, or tailed Pedipalpi, while the Tarantulidae constitute the remaining sub-order Amblypygi, the members of which are tailless.
Fam. 1. Thelyphonidae.[[254]]—This family comprises nine or more genera, differing chiefly in the position of the eyes, the structure of the genital operculum, the armature of the pedipalps, and the presence or absence of “ommatoids” in the anal segment.
The three following genera are among those most likely to be met with. Two ommatoids are present in each.
Thelyphonus has a spine on the second ventral plate, and a deep median impression on the male genital operculum, which is, however, absent from that of the female. There are about fifteen known species of this genus, inhabiting Southern Asia and the East Indies.
Typopeltis has ridges running forward from the lateral eyes. The middle third of the female operculum is raised and deeply impressed in the middle. This genus is represented in China and Japan. Mastigoproctus has a short and stout coxal apophysis of the pedipalp, without a tooth on its inner side. It is found in Mexico, Brazil, and the West Indies. Other genera are Thelyphonellus (Demerara), Labochirus (Ceylon), Hypoctonus (Burma), Mimoscorpius (Philippines), Uroproctus (Assam), Abalius (New Guinea), without ommatoids, and Tetrabalius (Borneo), with two pairs of ommatoids.