ing of the tube in the short segments would make little difference in its mode of action. Kirby and Spence were, I believe, the first to notice that an insect allied to the ants (Mutilla Europaea) has the power of making a sibilant, chirping sound, but they did not ascertain how this was effected. Goureau1 subsequently called attention to the same fact, and attributed it to friction of the base of the third segment of the abdomen against the second. Westwood, on the other hand, thought the sound was produced by the action of the large collar against the front of the mesothorax. Darwin, in his 'Descent of Man,' adopts the same view. 'I find,' he says,3 that these surfaces (i.e. the overlapping portions of the second and third abdominal segments) are marked with very fine concentric ridges, but so is the projecting thoracic collar, on which the head articulates; and this collar, when scratched with the point of a needle, emits the proper sound.' Landois, after referring to this opinion, expresses himself strongly in opposition to it. The true organ of sound is, he maintains, a triangular field on the upper surface of the fourth abdominal ring, which is finely ribbed, and which, when rubbed, emits a stridulating sound. It certainly would appear, from Landois' observations, that this structure does produce sound, whether or not 1 Ann. de la Soc. Ent. de France, 1837. ▲ Thierstimmen, p. 132. we consider that the friction of the collar against the mesothorax may also assist in doing so. Under these circumstances, Landois asked himself whether other genera allied to Mutilla might not possess a similar organ, and also have the power of producing sound. He first examined the genus Ponera, which, in the structure of its abdomen, nearly resembles Mutilla, and here also he found a fully developed stridulating apparatus. He then turned to the true ants, and here also he found a similar rasp-like organ in the same situation. It is indeed true that ants produce no sounds which are audible by us; still, when we find that certain allied insects do produce sounds appreciable to us by rubbing the abdominal segments one over the other; and when we find, in some ants, a nearly similar structure, it certainly seems not unreasonable to conclude that these latter also do produce sounds, even though we cannot hear them. Landois describes Fig. 8. Attachment of abdominal segments of Lasius flavus ☀ × 225. the structure in the workers of Lasius fuliginosus as having 20 ribs in a breadth of 0.13 of a millimetre, but he gives no figure. In Fig. 8 I have represented the junction of the second and third abdominal segments in Lasius flavus, × 225, as shown in a longitudinal and vertical section. There are about ten well-marked ribs (r), occupying a length of approximately of an inch. Similar ridges also occur between the following segments. 1 In connection with the sense of hearing I may mention another very interesting structure. In the year 1844, Von Siebold described 1 a remarkable organ which he had discovered in the tibia of the front legs of Gryllus, and which he considered to serve for the purpose of hearing. These organs have been also studied by Burmeister, Brunner, Hensen, Leydig, and others, and have recently been the subject of a monograph by Dr. V. Graber, who commences his memoir by observing that they are organs of an entirely unique character, and that nothing corresponding to them 2 Fig. 9. rt Tibia of Lasius flavus × 75. occurs in any other insects, or indeed in any other Arthropods. 1 Ueber das Stimm. und Gehörorgan der Orthopteren, Wiegmann's Art. f. Natur., 1844. 2 Die Tympanalen Sinnesapparate der Orthopteren,' von Dr Vitus Graber, 1875. I have therefore been very much interested by discovering (1875) in ants a structure which seems in some remarkable points to resemble that of the Orthoptera. As will be seen from a glance at Dr. Graber's memoir, and the plates which accompany it, the large trachea of the leg in the Orthoptera is considerably swollen in the tibia, and sends off, shortly after entering the tibia, a branch which, after running for some time parallel to the principal trunk, joins it again. See, for instance, in his monograph, plate ii., fig. 43; plate vi., fig. 69; plate vii., fig. 77 ; &c. Now, I have observed that in many other insects the trachea of the tibia are dilated, and in several I have been able to detect a recurrent branch. The same is also the case in some mites. I will, however, reserve what I have to say on this subject, with reference to other insects, for another occasion, and will at present confine myself to the ants. If we examine the tibia, say of Lasius flavus, Fig. 9, we shall see that the trachea presents a remarkable arrangement, which at once reminds us of that which occurs in Gryllus and other Orthoptera. In the femur it has a diameter of about of an inch; as soon, however, as it enters the tibia, it swells to a diameter of about 6 of an inch, then contracts again to, and then again, at the apical extremity of the tibia, once more expands to. Moreover, as in Gryllus, so also in Formica, a small branch rises from the upper sac, runs almost straight down the tibia, and falls again into the main trachea just above the lower sac. The remarkable sacs (Fig. 9, 8 s) at the two extremities of the trachea in the tibia may also be well seen in other transparent species, such, for instance, as Myrmica ruginodis and Pheidole megacephala. At the place where the upper tracheal sac contracts (Fig. 9), there is, moreover, a conical striated organ (x), which is situated at the back of the leg, just at the apical end of the upper tracheal sac. The broad base lies against the external wall of the leg, and the fibres converge inwards. In some cases I thought I could perceive indications of bright rods, but I was never able to make them out very clearly. This also reminds us of a curious structure which is found in the tibiæ of Locustidæ, between the trachea, the nerve, and the outer wall, and which is well shown in some of Dr. Graber's figures. On the whole, then, though the subject is still involved in doubt, I am disposed to think that ants perceive sounds which we cannot hear. The Sense of Smell. I have also made a number of experiments on the power of smell possessed by ants. I dipped camel's-hair brushes into peppermint-water, essence of cloves, lavender-water, and other strong scents, and suspended them |