316 PROCEEDINGS OF THE ACADEMY OF [May, 



land. The position I have taken is in direct opposition to the general 

 one as voiced by Korschelt and Heider, "that the Arachnida have 

 developed from the Paleostraca by adaptation to land life." 



6. The Taxonomic Rank of the Theraphos.e. 



By quite general consent arachnologists consider the Aranese thera- 

 phosse to be more primitive than the Aranese vera?. I do not know 

 whether this conclusion has at any time been critically discussed, and 

 in the present place I shall touch on it only briefly and tentatively, for 

 I feel my knowledge of the families of spiders is too deficient for me to 

 attempt to make any positive decision. 



The Theraphosse differ from the Aranese verse in having the chelicera 

 directed forward instead of downward, in possessing no trachese, and 

 in having no maxillary plates on the pedipalp (except in certain 

 Atypidse). 



We cannot say whether the character of the position of the chelicera 

 is more primitive in the first case than the other. The lack of maxillary 

 plates might or might not be due to degeneration, and we have seen 

 that there is no good basis for deciding whether lung-books are more 

 primitive than trachese. 



Thus these anatomical differences in themselves furnish no good 

 answer to our question. The Liphistiids in their general structure 

 appear decidedly primitive, with their four pairs of functional spin- 

 nerets and their segmented abdominal terga; yet Simon (1908) in his 

 recent description of the male of Liphistius birmanicus has shown 

 that the palpal bulbus is much more complex than in other Therapho- 

 sids. 



Excluding the Liphistiidse, the other families of the Theraphosse, 

 namely, the Aviculariidse and the Atypidse, would seem to be degenerate 

 in one respect, that of the spinnerets. For they possess neither colulus 

 nor cribellum, and almost all the Aviculariids lack also the anterior 

 spinnerets. The great length and appendage-like appearance of the 

 posterior spinnerets in the Aviculariids might not be a primitive 

 character, but be due to compensatory growth on account of the loss 

 of the anterior spinnerets. The general small size and compact group- 

 ing of the eyes might well be the result of the usual tubicolous mode of 

 life. Further, there are certain Aranese verse (such as Filistata) 

 which show the male copulatory bulbus less complex than in the 

 Theraphosse. 



In the loss of the spinnerets of the fourth abdominal segment, 

 in the small size of the eyes, and in the occasional great volume of 



