BRITISH WARBLERS
out to see what human creature was in misery. He found that it was a woman rejoicing over a meeting with her long-lost son. Here the respiratory changes and increased secretion in the lachrymal glands were the natural expression of joy." Similarity of the organic symptoms at different emotional periods may therefore be more common in animal life than we imagine, but it remains to be seen wherein exactly its true significance lies.
We will now compare the motor reactions of the more closely allied forms amongst the warblers, and for such a comparison we could scarcely choose a genus that could afford more suitable examples. The various species in some cases resemble one another so closely that it is only with difficulty that an expert with dried skins before him can detect the very slight differences in shading and form, and if it were not for some specific type of behaviour, recognition in their natural surroundings would be well-nigh impossible. As instances of extreme resemblance we may take the Willow Warbler and Chiff-Chaff, the Reed and Marsh Warbler, and the Sedge and Aquatic Warbler, and of those which can be readily distinguished, but nevertheless are very much akin, the Blackcap and Garden Warbler, the two Whitethroats, and the Grasshopper and Savi's Warbler. Since there is such resemblance in their outward appearance we naturally ask ourselves whether it also obtains in their instincts, habits, and emotions. Now we have no palaeontology to guide us as to the course mental evolution has taken, as we have in organic structures; the past is a sealed book, and I hold therefore that there is much to be learnt from such comparisons. In fact the only method left open to us is to examine and compare the results as they are presented in nature to-day, and decide whether they are such as we should expect to find according to the principles which we lay down. Let us first compare the instincts most familiar to us, namely those connected with reproduction. Both the Willow Warbler and Chiff-Chaff live in a similar environment and possess territories, the boundaries
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