Classification of the Spiders. 319 



The importance in the modifications in the organs of gene- 

 ration also appear to me to have been somewhat overestimated 

 bj Bertkau, That in the Dysderoidaj the testes and the 

 ovaries are united so as to form a ring*, just as in the Tetra- 

 pneumones, is a fact that shows, in combination with certain 

 other features in the organization of the Dysderoidas, tliat 

 these spiders are more allied to the Tetrapneumones than 

 are the other Dipneumones or Tristicta ; and this is also gene- 

 rally admitted. But to draw from these resemblances the con- 

 clusion that they are more nearly related to the Tetrapneu- 

 mones tlian to the Tristicta is, I think, erroneous, as the 

 Dysderoidas agree with the Tristicta not only in the direction 

 in which the claw of the mandibles moves, and in the number 

 of the joints of the inferior spinners, but also in their having 

 only one pair of air-sacs — a character which, as I have already 

 remarked, ought to have been, more particularly with Bertkau, 

 of the most essential importance, and ought to have prevented 

 him from separating the Dysderoid^ from the other Dipneu- 

 mones and uniting them with the Tetrapneumones. That the 

 Dysderoidffi have, in tlieir general habitus, a striking resem- 

 blance with many Drassoidaj, cannot well be denied. 



A character which, in Dr. Bertkau's classification, is of a 

 certain importance for the limitation of the families, is taken 

 from the different number (and the form) of the female's 

 receptacula senmiis. Thus the Tetragnathoida? (Pachygna- 

 thida3, Bertk.) differ from the Epeiroida3 and the Theridioidge 

 in having three such receptacles, not two only [A, p. 401). 

 Their common opening is situated, together with the orifice of 

 the oviducts, far (more or less) behind the spiracles ; and this 



characterization of thedift'erent spider-groups, the chief stress on anatomical 

 features, as this reason may to many persons seem to be of great weight, 

 viz., tlie practical difficulties of determining, by means of such features, 

 the systematic place of an nnlinown spider. And that these difficulties 

 really exist, is seen, for instance, from the fact that nian}^ of the statements 

 concerning the structure of the respiratoiy organs &c. given by such an 

 experienced anatomist as jNIenge are, by Bertkau, shown to be erroneous. 

 Moreover, it will, with the method in question, often be necessary to destroy 

 the specimen that is to be determined, even in those cases where it belongs 

 to a very rare species, or is a " unicura," and this is also a drawback of prac- 

 tical importance. But it may be objected against these remarks, that the 

 aim of a natural system is not that of facilitating the determination of 

 the different species, but of giving an expression of their real affinities ; 

 and this is true — though there might perhaps be found some means of 

 reconciling botli these claims. At least it would seem that if an anato- 

 mical feature really is of great systematic importance, there exists also 

 some external feature that corresponds to it. 



* In Tegenaria domestica also the ovaries form, even till shortly before 

 the maturity of the animal, a perfect ring (see Dahl, " Analytische Bear- 

 beitimg, etc.,'' loc. cit. p. 4). 



22* 



