1902 Encyclopedia > Arachnida > Arachnida - Order VI: Thelyphonidea - Introduction

(Part 20)




The last group, Scorpions, seems to be the culminating point of the Arachnids in a certain plane, and it presents the archnidous type in its highest and most complex state of development. The group now to be considered gradually lowers, so to speak, this type again through its three well-marked families, to the last order Araneidea.

As has been before observed, there is seldom or never in nature exactly the same hiatus between one group and another, as there may be between either of them and others; or, in other words, some groups are far more nearly allied to the one next to it than others are to that next to them, although, perhaps, all of these groups bear the same apparent value in a systematic arrangement. Thus, for instance, the groups A,B,C,D, may all be equal in a systematic arrangement, and yet A and B may be far more nearly allied than B and C; or again, C and D may be more closely united than either B and C or A and B. So the two order of Arachnids - Scorpionidea and Thelyphonidea - are certainly far more nearly allied to each other than, for instance, the Solpugidea and Scorpionidea, or the Thelyphonidea and Araneidea are to each other respectively. So obvious is the affinity of the family Thelyphonides of the present order to the Scorpiones, that Walckenaer and others have included them in the same order, making a separate order of its other family, Phrynides; but the later family certainly seems nearer to Thelyphonides than even the Thelyphonides to the Scorpiones; and so, while the Thelyphonides and the Phrynides must go together, these last could scarcely with any propriety be included in the same order as the scorpions. This will, we think, be evident when we consider presently their structural characters. From these and other considerations, it has therefore been thought best to separate the Thelyphonides from the Scorpionides, and include them in another order with Phrynides.

In the order Thelyphonidea, the cephalo-thorax is similar in the general nature and condition of its integument to that of the scorpions, being hard, granulose, and sometimes tubercular, bearing also visible traces of its soldered segments.

The abdomen is segmented, and united to the cephalo-thorax by a pedicle of greater or less strength, but never, as in the Scorpiones, throughout its entire breadth; it terminates in one family (Thelyphonides) with three post-abdominal segments, to which is attached a long multi-articulate setiform tail; in another (Tartarides) with a short tail of different form according to the species; and in the third family(Phrynides) the abdomen terminates with a simple button-like segment.

The legs of the first pair are much longer than the rest (in the Phrynides of most inordinate length) and antenniform; the tarsi, and generally the metatarsi, multi-articulate, ending without any terminal claw; the legs of the other three pairs are seven-jointed, with the last, or tarsal joint, subdivided.

The eyes when present (as in two families) are eight in number, placed on the fore part of the cephalo-thorax in three groups, and forming a triangle with the apex (more or less acute) directed forwards; the base of the triangle is formed by two lateral groups, each of three continuous eyes; the apex by the third group of two eyes near together, but not generally contiguous to each other.

The facles are monodactylous, or terminating with a simple movable fang. The palpi are four-jointed, monodactylous, or rather didactyle in a modified form. The sternum is more developed than in the scorpions, but not so fully as in the next order, Araneidea. The labium is either entirely wanting or very rudimentary in one family, in another fairly developed, and in another altogether absent. In any case, it is probably of small economic importance compared to the labium in the Araneidea.

Such knowledge as is at present attainable in regard to the internal anatomy of this order will be noted in the separate descriptions of each family. These families are three in number, -- Thelyphonides, Tartarides, and Phrynides, -- and being very distinct, it will be well to give a short diagnosis of each.

Read the rest of this article:
Arachnida - Table of Contents

About this EncyclopediaTop ContributorsAll ContributorsToday in History
Terms of UsePrivacyContact Us

© 2005-23 1902 Encyclopedia. All Rights Reserved.

This website is the free online Encyclopedia Britannica (9th Edition and 10th Edition) with added expert translations and commentaries