CONSTRUCTING BRIDGES, 245 
1 now increased the length to 16 feet, and watched 
her while she made thirty journeys backwards and 
forwards. She also brought during the time seven 
friends with her. 
It surprised me very much that she preferred to go 
so far round rather than to face so short a drop. 
In illustration of the same curious fact, I several 
times put specimens of L. niger on slips of glass raised 
only one-third of an inch from the surface of the nest. 
They remained sometimes three or four hours running 
about on the glass, and at last seemed to drop off 
accidentally. 
Myrmica ruginodis has the same feeling. One 
morning, for instance, I placed one in an isolated 
position, but so that she could escape by dropping one- 
third of an inch. Nevertheless at the same hour on 
the followiag morning she was still in captivity, having 
remained out twenty-four hours rather than let herself 
down this little distance. 
Again I filled a saucer (woodcut, Fig. 11, s) with 
water and put in it a block of wood (w), on the top of 
which I fastened a projecting wooden rod (B), on the 
end of which I placed a shallow glass cell (a) containing 
several hundred larve. From this cell I allowed a slip 
of paper (P) to hang down to within “3, of an inch 
of the upper surface of the nest. At one side I put 
another block of wood (c) with a lateral projection 
(Dd) which hung over the cell containing the larve. 
J then made a connexion between D and 4, so that ants 
