Among fishes I have found but few sounds, and most of these I have never heard except when the fish was taken out of the water. The carp and high-fin, however, I have frequently heard while in the water. It has occurred to me that the sound is not the medium of communication, but it is the result of an action by which they do communicate even when the sound is not audible. I have observed while holding the fish in my hand when he makes this sound that it produces a jarring sensation which is very perceptible. It is quite possible that in his natural element these powerful vibrations are imparted to the surrounding water, and through it communicated to another fish, who feels it in his sensitive body instead of hearing it as sound. It may be accompanied by the sound merely resulting from the force applied, but not in itself constituting any part of the means of communication. It is not unlike what we call sound, in the fact that it is generated in the same way, transmitted in the same way, and received in the same way as sound. When I have time and opportunity I shall carry my studies of the language of fishes much farther. Their means of communication are very contracted, but it is superfluous for me to say that they have such means. Many observations have already been made on the language of insects, and much diversity of opinion prevails. Very little has been said about the details of their intercourse, but the consensus of opinion is that they must in some way communicate among themselves. To me they seem to live within a world of their own, as other classes of the animal kingdom do. The means of communication used by mammals could not be available among aquatic forms, any more than could their modes of locomotion. Each different class of the animal kingdom is endowed with such characters and faculties as best adapt them to the sphere in which they live; and the mode of communication best fitted to the conditions of insect life would be as little suited to mammals, perhaps, as the feathers of a bird would be for locomotion in the realm of fishes. [Sidenote: LANGUAGE OF INSECTS] I am aware that some high authorities have claimed that insects communicate by sounds. My own opinion is that they employ a system of grating or scratching by means of their stigmata, but that the sound created thus performs no function in the act of communicating, but is only a bi-product, so to speak, and that the jarring sensation transmitted through the air is the real means by which they understand each other, possibly somewhat like telegraphy, in which the sounds are not modulated, but are distinguished by their duration and the interval between them. I do not announce this as conclusive, but merely suggest it as a possible key to their mode of intercourse. [Sidenote: A COLONY OF ANTS]