188 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 
Pholeus; 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 16 seems a 
poor spider after the dynamical and migratory 
gossamer; but it happens, curiously enough, that a 
