It is difficult to determine the range of hearing in the lower organisms. But it is quite possible, nay, very probable, that the superior limit of auditory sensation is much more extended in insects than it is in man. We know that many insects, such as the cicadas, the crickets and grasshoppers, many beetles, the death's-head moth, the death-watch, and others, make, in one way or another, sounds audible to us. But there may be many insect-sounds--we may not call them voices--which, though beyond our limits of hearing, are nevertheless audible to insects. At the other end of the scale, on the other hand, slow pulsations may be appreciated--for example, by aquatic creatures--by means of what we term the auditory organs, in a way that is not analogous to the sensation of sound in us. It may be noted that auditory organs are dotted about the body somewhat promiscuously in the various invertebrates. We have seen that auditory organs, or what are generally believed to be such, are found in the foot of bivalves, in the antennules of lobsters, in the fore legs of crickets and ants, in the abdomen of locusts, in the balancers of flies, and in the tail of _Mysis_. But when we come to consider the matter, there is no reason why the organ of hearing should be in any special part of the body. The waves of sound rain in upon the organism from all sides. There is no great advantage in having the organs of hearing in the line of progression, as with sight, where the rays come in right lines; nor in having them in close association with the mouth, as in the case of the organ of smell. Closely connected with the organ of hearing in vertebrates is the organ of another and but recently recognized sense. In briefly describing the auditory apparatus in man, mention was made of three curved membranous loops, the so-called semicircular canals. A few more words must now be said about them and the membranous sac with which they are connected.