Fig. [228].—Cryptocellus simonis, × 4. (After Hansen and Sörensen.)
In 1838 Guérin-Méneville[[339]] described an Arachnid from West Africa which he named Cryptostemma westermannii. At rare intervals occasional specimens of allied forms have been taken in the same region until six species of Cryptostemma have been established. In South America, also, two unique examples of very similar creatures are the only known representatives of the two species of the allied genus Cryptocellus. All the examples hitherto found are of fair size (between ⅕ inch and ½ inch in length), and bear some general, though superficial, resemblance to the Trogulidae, which has led to their being placed among the Phalangidea by almost all the Arachnologists who have noticed them. Their claim to this systematic position, however, is extremely doubtful, and Hansen and Sörensen, who have had the opportunity of studying the group much more minutely than previous writers, are of the opinion that they ought to constitute a separate order of Arachnids, more nearly allied to the Pedipalpi than to the Phalangidea. In this place it is only possible to indicate some of their peculiar characteristics. Their integuments are particularly hard and coriaceous. The cephalothorax is united to the abdomen by a rather broad pedicle, but there is also a remarkable coupling apparatus which makes the constriction between cephalothorax and abdomen appear very slight. There is a movable anterior projection of the cephalothorax, the “cucullus.” The two-jointed chelicerae terminate in minute chelae, as also do the five-jointed pedipalps. There are no spiracles on the abdomen, but two are situated on the thorax above the coxae of the third pair of legs. Perhaps the most remarkable fact is that, as in the Araneae, a modified limb is used by the male for the fertilisation of the female; but in this case it is not the tarsus of the pedipalp, but of the third leg of the male, which is specially developed as an intromittent organ.
Ordinal rank is not universally accorded to the group, but whatever its true position, the known forms fall under a single family Cryptostemmatidae, including the two genera Cryptostemma and Cryptocellus.
Order VIII. Phalangidea (Opiliones).
Tracheate Arachnids, with abdomen united to the cephalothorax by its whole breadth. They are oviparous, and undergo no metamorphosis. Abdomen always segmented. A pair of odoriferous glands opening on the thorax. Two simple eyes; three-jointed chelate chelicerae; pedipalpi not chelate. Spinning organs absent.
“Harvesters,” “Harvestmen,” or “Harvest-spiders,” as these animals are popularly called, need never be confounded with true Spiders if the absence of a constriction between the cephalothorax and abdomen be noted. They are more difficult to distinguish from Mites, members of which group have sometimes been described as Phalangids. The Phalangid is, however, generally recognisable by its segmented abdomen, and as a further point of distinction, it may be noted that, whereas the anal orifice is always transverse or circular in Phalangids, it is uniformly longitudinal in the Acarines.
Fig. [229].—Oligolophus spinosus. (After Pickard-Cambridge.)
Members of this group vary considerably in habit. The best known forms are exceedingly active, and trust to their speed in endeavouring to escape from danger, at the same time emitting an odorous fluid from two apertures situated just above the coxae of the first pair of legs. These active Harvestmen are only found in the mature state at certain seasons of the year, and are believed, therefore, to live only for a single season. Slow-moving forms, like the Nemastomatidae and the Trogulidae, which live amidst grass and herbage, have a much longer duration of life. In danger they remain perfectly still, and trust to their earthy appearance to escape observation.