13i AXXALS XEW YORK ACADEMY OF SCTEXCES 



However, there is more to the distribution of spiders than wind. We 

 need an explanation of the remarkable' discontinuities which have been 

 pointed out. 



Ocean drift is frequently brought in to explain distribution and it has- 

 probably been the eifective agent in many instances. The opponents of 

 such an idea forget the long ages iii which accidental drift has had a. 

 chance to work. However, the ease with which large numbers of spiders 

 take to the air every year makes recourse to the small numbers that mav 

 make successful voyages on driftwood unnecessary. 



Then there is man. Hardly a ship sails from port without araneid 

 stowaways, and inland shipments of freight also carry their quota, but 

 these are nearly always a certain few species of which only those that live 

 about man's dwellings are likely to become established. Xone of the 

 "tarantulas"' which come in nearh' every shipment of bananas have be- 

 come a part of the Xew York fauna. Furthermore it is very unlikely 

 that the distribution of most spiders has changed much since man began 

 to sail the seas. The study of their movements must go far back of that. 



One takes up the question of land bridges with something akin to a 

 groan since opinion on the matter is so diverse and the evidence, whether 

 pro or con, about a given bridge is often so slight. Paleontology offers 

 little direct evidence as to the ancient movements of spiders since so few 

 fossil spiders are known. Several have been described from the Carbon- 

 iferous of both hemispheres and probably at least one genus (Artliroly- 

 cosa) was even then found in both Europe and Xorth America. The 

 only living genus of the tyipe of spiders which was apparently common 

 in Carboniferous is Liphistiis. It is found now only in the islands of 

 Pinang and Sumatra. 



Spiders with unsegmented abdomens, that is all living spiders except 

 Lipisiius, may not have arisen until the Mesozoic, but, if so, evolution 

 was fairly rapid, for most of the Oligocene and Miocene spiders belong- 

 to present-day families and even genera. 



E. T. Pocock^' gives an interesting analysis of the ancient movements 

 of spiders. A few of the present-day distributions given by him differ 

 from those given by other authorities, but none of the differences which T 

 have noticed would materially change his argument. In his section on 

 the "Distribution of some of the Families of Arachnomorph^ that were 

 represented in the Oligocene Period'' he mentions seventeen genera found 

 in amber which are still living. While it is perfectly true that "although 

 since the Oligocene these Spiders have had the same time for dispersal, 

 they nevertheless differ greatly in their distribution,'' the implication that 



I'Proc. Zool. Soc. London. 1903. I. pp. 340-368. 



