TRAP- DOOR SPIDERS. 247 



existing forms of life will be traced with snfGcient 

 accuracy to enable us to follow on the map the lines 

 along which affinity travels ; and thus point out at 

 once the probable relationship between two given 

 forms, and also the route by which they reached their 

 present stations. Eecords of local varieties, and the 

 careful discrimination between forms which have 

 small but permanent points of difference, thus acquire 

 an importance which they would not otherwise possess. 



The geographical distribution of trap-door spiders 

 is of j)eculiar interest on account of the sedentary 

 habits maintained during life by the females. Most 

 animals are capable of travelling long distances, or of 

 being accidentally transported from place to place in 

 such a way that colonies are frequently established 

 far away from the parent settlement, and we are left 

 in the dark as to whence they came and who are their 

 nearest relations. But, in the case of spiders inhabi- 

 ting true trap-door nests, this is not so ; they begin 

 life immediately on leaving the parent nest by 

 making hemes for themselves near at hand which 

 they will not desert, and there is no likelihood of 

 their being accidentally carried from place to place 

 unless occasionally by running water. Thus it hap- 

 pens that whenever we find the same trap-door 

 spider at two distant localities, we may feel tolerabl}'" 

 sure that the species has travelled from one to the 

 other by gradual extension, and that, either now or 

 in times past, it occupied all the intervening country. 



For instance, we find Nemesia Eleanora at Mentone, 

 and again at Cannes, while it has not yet been 

 detected at Nice, Antibes, nor any other intermediate 

 point ; but according to this hypothesis, this species 



