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The Classification of Spiders 1

1887; Nature Portfolio; Volume: 36; Issue: 914 Linguagem: Inglês

10.1038/036012a0

1476-4687

O. P. Cambridge,

Lepidoptera: Biology and Taxonomy

ALTHOUGH Dr. Thorell's paper is nominally only a criticism of Dr. Bertkau's views, it is really a masterly sketch of the literature on the subject of the classification of spiders, and a review of the methods of various authors from Lister downwards. The two leading views at present held on this subject appear to be represented by the author (Dr. Thorell) and Dr. Bertkau. These two views may be stated generally as anatomical v. biological, the former being the basis of Dr. Bertkau's classification, the latter (combined with considerations of external structure) that of Dr. Thorell. Dr. Thorell successfully, as it appears to us, defends the classification provisionally adopted in 1869, in his work “On European Spiders,” from the sweeping charge that it is neither natural nor equal, nor based on characters of sufficient importance and distinctly expressed, though at the same time he freely admits its inevitable imperfection. He shows that in no branch of Nature are the subordinate groups of exactly equal value, nor should it be expected that the same equal systematic value would be found in the subordinate groups of the class Arachnida. It is well to remember that zoologists have to form their groups out of such materials as have come to their hands ready provided for them by Nature. They cannot expect to advance natural science by constructing out of limited materials a perfectly symmetrical system, and then insisting that all the diverse forms of Nature shall, nolens volens, be stuffed somewhere or other into it. Equality, therefore, of systematic value in the various groups into which spiders (Araneidea) may be divided can at best be only approximate; and it seems evident that as our knowledge of structure, whether external or internal, or of habits as dependent on and arising out of structure, becomes more extensive and exact, so some further modifications may become necessary in the primary divisions of spiders. After subjecting Dr. Bertkau's classification (which is based principally on the breathing-organs) to a minute and destructive criticism, Dr. Thorell modifies his former views by reverting, in some measure, to the Latreillian division of spiders into (1) those possessing four air-sacs, Tetrapneumones; (2) those with two, Dipneumones; still, however, retaining the old Latreillian biological divisions, Territelariæ, Tubitelariæ, Orbitelariæ;, &c., based on habits, because the groups so divided may yet be thoroughly and scientifically differentiated by important and trustworthy structural characters. These divisions (now called by Dr. Thorell “tribus ”) are, as is well known, seven in number, and each is subdivided into families, which, with few exceptions, include only European species, Dr. Thorell's opportunities for the study of exotic groups not enabling him to construct a more complete subdivision of all known spiders. Dr. Bertkau's primary division of the Araneidea is into two groups, called suborders—Tetrasticta, with four breathing-apertures, and Tristicta, with three. Dr. Thorell shows conclusively, that in the present state of our knowledge of the respiratory system of spiders (though this is far advanced beyond what it was in Latreille's days, and in a great degree the advancement is admitted to be due to Dr. Bertkau's labours) these two suborders are artificial rather than natural; as are also his subdivisions of the Tristicta, which are based on the undoubtedly remarkable characters to which such great prominence was given by the late Mr. Blackwall, that is, the possession or absence of a cribellum and calamistrum, the use of these in primary subdivision bringing together spiders not closely allied by any other natural characters. Dr. Thorell attributes a certain amount of classificatory importance to these organs by his intercalation of the families of his largest “tribus” possessing them, in a kind of osculant or collateral way, and of the other “tribus” in which they are found, in a linear arrangement, guided, however, in both cases by their possessing such other characters as, in all instances, fully warrant the position assigned to them. The anatomical study of the tracheœ (properly so called) of spiders seems to be yet in its infancy. Certainly at present these organs of respiration do not appear to warrant the importance attributed to them by Dr. Bertkau; and although Dr. Thorell's primary subdivisions are, in their names, strictly speaking, based on only biological characters, yet in reality they severally enshroud the most important structural ones, and hold all known spiders in a fairly natural system. They are, moreover, well known, and appear likely to be adopted for some time yet to come, with more or less modification, by the majority of araneologists.