VII. 



The Classification of Arachnids. 



^TATURALISTS have long looked forward to a day when the 

 systematic arrangement of living creatures will exhibit the real 

 relationship which they bear to one another. All honest classificatory 

 work helps science to realise this great ideal, but much is of the nature 

 of raw material which may long remain without apparent use. Occa- 

 sionally, however, we meet with contributions which seem to add 

 considerably, and at once, to the progress of the work ; and such are 

 several recent memoirs on the spiders and their allies. 



In 1851, Schiodte described a new genus of Malayan spiders, 

 Liphistius, of most remarkable structure. This genus was at first 

 classed with the Territellariae — the tribe which includes ihe trap-door 

 species, and the well-known large hairy " bird-killers " of the tropics. 

 More recently Thorell has considered that the genus should form a 

 tribe by itself, but be included with the Territellariae in the sub-order 

 Tetrapneumones, or spiders with four lung-sacs ; and now Pocock 

 (i) gives good reasons for assigning to Liphistius a s'ill greater classifi- 

 catory value, and placing it in solitary grandeur over against all other 

 known spiders. Several striking characters seem to support this 

 view. The abdomen in other spiders has lost neatly all traces of 

 segmentation, but Liphistius exhibits nine dorsal and two ventral 

 sclerites. The spinning-mammillae, which in other spiders leave their 

 embryonic position as ventral appendages of the abdominal sternites 

 behind the lung-sacs, and migrate to the extreme apex of the abdo- 

 men, retain in Liphistius their primitive place beneath the middle of 

 the abdomen. This latter character suggests the names proposed by 

 Pocock for his new divisions, the species of Liphistius being called 

 Mesothelae, and other spiders Opisthothela'. His primary division 

 of these latter tallies with the old classification into Tetrapneumones- 

 and Dipneumones, but he agrees with Simon that the relationships of 

 a genus [Hypochilus) of four-lunged spiders are with the latter rather 

 than with the former group, and, therefore, suggests the terms 

 Mygalomorphae and Arachnomorphae to supersede those time- 

 honoured names. In all spiders of the latter group (except Hypochilus} 

 the hinder pair of lung-sacs are replaced by tracheae. Liphistius 

 agrees with the Mygalomorphae in having four lung-sacs, but, in 

 several points, it shows affinities with the other division. Alone 



