312 Prof. T. Thorell on Dr. BerthaiCs 



3. It by no means rarely happens that in groups that are 

 highly specialized and very rich in species no sharp limits 

 can be drawn between the different lower groups into which 

 they must be divided. This must especially be the case with 

 the order of the Spiders, on account of the peculiarities in the 

 bodily structure of these animals, peculiarities of which we 

 have spoken above (p. 306), and which make their classification 

 so difficult. Even amongst the most natural coordinate 

 groups we find examples of some one of them being united 

 with another by "transition-forms" the systematic position of 

 which must, by sad necessity, be more or less uncertain ; and 

 the consequence of this is, that when we have, for some prac- 

 tical pur])ose (as in my work ' On Eur. Spid.'), to define such 

 groups by means of a single or a few characters, these become 

 either artificial or of subordinate weight, or even assume a nega- 

 tive form. Such groups (and to them belong the tribus of the 

 Dipneumones) should therefore, as has already been insisted 

 upon, rightly be determined by means of a more detailed ex- 

 position of the structure of their different parts, with indica- 

 tions of the exceptions from all the characters given. And it 

 will then be the preponderating importance and number of the 

 characters by Avhich a given form, for instance a genus, agrees 

 more with the one tlian with the other of the groups in ques- 

 tion, that decides to which of them it ought to be referred. 

 In such cases the choice sometimes depends on individual 

 appreciation, and the systematic place of the genus may thus 

 appear to be " vacillating ; " but this cannot well be avoided, 

 nor would it seem to be of much consequence. Though, 

 for instance, tlie Laterigradse are a natural group, it is scarcely 

 possible to draw a sharp limit between them and the Tubi- 

 telarise, or rather between the Heteropodoidte (Sparassidse, 

 Bertk.^ and the Drassoidaj. Through the Thomisoidse, the 

 Laterigradse also approach the Epeiroidaj of the tribus Orbite- 

 larise. The Lycosoidge are not only nearly allied to the Dras- 

 soidge [Zora^ for instance), but they pass (through, for instance, 

 SphedanuSf Thor.) gradually and almost imperceptibly into 

 the Agalenoidffi, and might therefore seem to be more closely 

 allied to this last-named family than to the Oxyopoidte, which 

 belong to the same tribus as the Lycosoid^ (Citigradaj), nay, 

 are even regarded by Bertkau as a mere subfamily of the 

 Lycosoidse. Epeiroidas and Theridioidge are held to be dif- 

 ferent families even by Bertkau, notwithstanding that he 

 considers [A, p. 401) " the different form of the iceb to be the 

 essential and most important character by which these two 

 families may be distinguished from one another." I think 

 therefore that it would scarcely be just to reject the old and 



