Classification of the Spiders. 315 



Bertkau, when he di'evv the characteristics for dividing the 

 Spiders into two suborders from differences in their breathing- 

 organs, would, in conformity with Dufour, have divided them 

 into such as breathe only with air-sacs, and have two pairs of 

 these organs, and those in which the posterior pair of air-sacs 

 is replaced by tracheae, and which therefore have only o«e pair of 

 air-sacs. But instead of that he has, as I have already 

 stated, chosen as the chief basis for his classification the 

 number of the openings through which these different organs 

 of respiration communicate with the exterior, and thus di- 

 vided the Spiders into the two suborders, Tetrasticta w'liYi four ^ 

 and Tristicta with three breathing-holes or spiracles. Ac- 

 cordingly he has separated the Dysderoida^ from the rest of the 

 Spiders that have only one pair of air-sacs, or thcDipneumones, 

 and united them with the Tetrapneumones or Territelarice 

 in his suborder Tetrasticta. But this new arrang-ement does 

 not appear to be at all a natural one ; the different number 

 and position of the spiracles have not nearly the gi'eat sys- 

 tematic importance that Bertkau attributes to these charac- 

 ters. How untenable, in fact, is the basis for his two suborders, 

 is demonstrated by the fact that Bertkau refers to his Tri- 

 sticta two genera belonging to two widely different families, 

 viz. PholcuSj Walck. {A^ p. 398) and Ctenium^ Menge*, in 

 which, according to Bertkau's own discoveries, the unpaired 

 spiracle and its trachea are completely loanting \ Consistently 

 he ought to have formed for the reception of these spiders a 

 separate suborder, Disticta \ but he would then have been 

 obliged to separate Ctenium from the rest of his Therididee, 

 and to place this genus in the vicinity of Pholcus'\^ which, of 

 course, could not be done in a " natural " classification. As 

 to the unpaired spiracle, it no doubt corresponds to the two 

 posterior spiracles in the Dysderoida^, or, in other words, the 

 two posterior spiracles of the Dysderoidce are in the Tristicta 

 moved more or less hachivard^ and are more or less intimately 

 united with each other. This is proved not only by the fact that 

 the unpaired spiracle is often, especially when situated further 

 forward, evidently formed of two coalesced spiracles, but also 

 by the tracheaj which debouch through this spiracle being, as 

 in the Dysderoidaiij:, one or two on each side, though in the 



* See [Foi'ster and] Bertkau, " Beitrage zur Keuntniss der Spinnen- 

 fauna der liheinprovinz," in Verhaudl. des naturhist. Vereius der preus- 

 sischeu Rlieiulande und AVestfaleus, Jahrg. xl. (4 Folge, x.), p. 349 

 (1883). 



t Bertkau remarlrs {A, p. 398) that the tarsi of Pholciis opilionoides 

 are subdivided into a rather large number of small joints ; the same had 

 been shown to be the casein Fh. puUulns, Hentz. See Thorell, "Descript. 

 of the Araneae collected in Colorado, &c.," loc. cit. p. 488. 



X Compai-e Menge, ' Preussische Spiunen,' pp. 298 and 300. 



