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The aquarium-maze used in training part of the fish to come forward and part to go to the rear to be fed 164 35. Cyprinodon learn to move in a body more readily than to split into two separate groups 165 36. Goldfish learn more readily if accompanied by a trained leader 37. An aquarium-maze arranged to test the power of observation of fish 38. Goldfish react more rapidly if allowed to watch others perform^1 39. Flocks of hens are organized into a definite social hierarchy 40. Cockerels also have a social organization 209; principle of,

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demonstrated clearly the protective value of numbers of animals as compared with single individuals when exposed to equal volumes of colloidal silver suspension of the same concentration. Allee and Schuett ('27) confirmed and extended these experiments. Mass protection from the toxic effects of colloidal silver has been demonstrated by these workers for a wide range of animals, including, among others, various Protozoa, planarians, leeches, ophuroid starfishes, crustaceans, and frog tadpoles. Drzewina and Bohn originally interpreted their results as being due primarily to the more rapid production of some autoprotective substance by the group than by the isolated individuals, which acted by some other means than the fixation of the toxic materials. The experiments of Allee and Schuett indicated that, under the conditions of their experiments, a major part of the protection furnished by the mass was due to the more rapid adsorption of the toxic colloidal silver either directly on the surface of the animals or upon the slime which the animals had shed into the surrounding medium, but their experiments did not prove conclusively that the observed protection was due entirely to such adsorption.

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