44 ARRANGEMENT OF CHAMBERS. 
represents garden mould, which the ants have them- 
selves excavated, as shown in the figure. For the 
small doorway (a), indeed, I am myself responsible. 
I generally made the doorways of my nests narrow, so 
as to check evaporation and keep the nests from 
becoming too dry. It will be observed, however, that 
behind the hall (6) the entrance contracts, and is still 
further protected by a pillar of earth, which leaves on 
either side a narrow passage which a single ant could 
easily guard, or which might be quickly blocked up. 
Behind this is an irregular vestibule (c), contracted 
again behind into a narrow passage, which is followed 
by another, this latter opening into the main chamber 
(d). In this chamber several pillars of earth are left, 
almost as if to support the roof. Behind the main 
chamber is an inner sanctum divided into three cham- 
bers, and to which access is obtained through narrow 
entrances (f, f, f, f). Most of the pillars in the main 
chamber are irregular in outline, but two of them 
(g, g) were regular ovals, and round each, for a distance 
about as long as the body of an ant, the glass had been 
most carefully cleaned. This was so marked, and the 
edge of the cleaned portion was so distinct, that it is 
impossible not to suppose that the ants must have 
had some object in this proceeding, though I am unable 
to suggest any explanation of it. 
I have already mentioned (ante, p. 23), that there 
is evidence of some division of labour among ants. 
Where, indeed, there are different kinds of workers, 
