1 88 The Naturalist in La Plata. 



I found them in greatly increased numbers : on the 

 tops of cardoons, posts, and other elevated situa- 

 tions they were literally lying together in heaps. 

 Most of them were large and of the olive-coloured 

 species ; their size had probably prevented them 

 from getting away earlier, but they were now float- 

 ing off in great numbers, the weather being calm 

 and tolerably dry. To-day I noticed a new species 

 with a grey body, elegantly striped with black, and 

 pink legs a very pretty spider. 



"26th. Went again to-day and found that the 

 whole vast army of gossamers, with the exception 

 of a few stragglers sitting on posts and dry stalks, 

 had vanished. They had taken advantage of the 

 short spell of fine weather we are now having, after 

 an unusually wet and boisterous autumn, to make 

 their escape." 



Here it seemed to me that a conjunction of cir- 

 cumstances first, the unfavourable season prevent- 

 ing migration at the proper time, and secondly, the 

 strip of valley out of which the spiders had been 

 driven to the higher ground till they were massed 

 together only served to make visible and evident 

 that a vast annual migration takes place which we 

 have only to look closely for to discover. 



One of the most original spiders in Buenos Ayres 

 mentally original, I mean is a species of 

 Pholcus; a quiet, inoffensive creature found in 

 houses, and so abundant that they literally swarm 

 where they are not frequently swept away from 

 ceilings and obscure corners. Certainly it seems a 

 poor spider after the dynamical and migratory 

 gossamer ; but it happens, curiously enough, that a 



