I shall now bring these numerous instances to a close with a quotation from Mr. Belt, which reveals in the most unequivocal manner surprising powers of observation and rational action on the part of the leaf-cutting ants of South America, whose general habits we have already considered:-- A nest was made near one of our tramways, and to get to the trees the ants had to cross the rails, over which the waggons were continually passing and repassing. Every time they came along a number of ants were crushed to death. They persevered in crossing for some time, but at last set to work and tunnelled underneath each rail. One day, when the waggons were not running, I stopped up the tunnels with stones; but although great numbers carrying leaves were thus cut off from the nest, they would not cross the rails, but set to work making fresh tunnels underneath them. _Anatomy and Physiology of Nerve-centres and Sense-organs._ The foregoing facts concerning the intelligence of ants fully justifies Mr. Darwin's observation that 'the brain of an ant is one of the most marvellous atoms of matter in the world, perhaps more so than the brain of a man.' It may therefore be interesting in this particular case to depart from the lines otherwise laid down throughout the present work, and to devote a short section to the anatomy and physiology of this nerve-centre with its appended organs of sense. The brain of an ant, then, is proportionally larger than that of any other insect. (See Titus Graber, 'Insects,' vol. i. p. 255.) In structure, also, the brain of an ant is in advance of that of other insects, its nearest analogue being the brain of a bee. The superiority of development is particularly remarkable with reference to the 'stalked bodies' of Dujardin; and these are largest in neuter workers, which are the most intelligent members of the community. Injury of the brain causes, as in higher animals, tetanic spasms and involuntary reflex movements, followed by stupefaction.