Fig. 276.—Antennal pit of Melolontha vulgaris, seen in vertical section.—After Hauser.

Very remarkable pits occur in the antennal lamellæ of Melolontha vulgaris (Fig. 275) and other lamellicorns. On the outer surface of the first and seventh (in the female the sixth) antennal leaf, as also on the edges of the other leaves, only arise scattered bristles; on the inner surface of the first and seventh leaves, as also on both surfaces of the second to sixth leaves, are close rows of rather shallow depressions of irregular form, some circular, others regularly hexagonal. Their number is enormous: in the males 39,000, in the females about 35,000, occur on each antenna.

Fig. 277.—Organ of smell of Anophthalmus.—After Hauser. A, a, b, the same in A. tenuis, B in A. tellkampfii.

Fig. 278.—Section through antennal joint of Vespa crabro, showing the great number of olfactory pits, olfactory and tactile bristles. A, section through an olfactory pit of Vespa crabro.—After Hauser.

The antennal pits and teeth of Dyticus marginalis are morphologically and physiologically identical with those of bees and wasps. In Anophthalmus bilimekii, Hauser found on the last antennal joints about 60 teeth, which essentially differ in form from those previously described; they are very pale, transparent, cylindrical, elongated, and bent elbow-shaped on the first third, so that the last two-thirds run parallel with the antenna. The length of these remarkable teeth is 0.035 mm., their breadth 0.005 mm. He only found them in Anophthalmus, and in no other species of Carabidæ; they must resemble the teeth described in Chrysopa. Our species possesses similar processes (Fig. 277). Similar teeth occur on the maxillary and labial palpi of beetles. Dyticus marginalis possesses at the end of each terminal palpal joint a group of very small teeth, which were also detected in Anophthalmus bilimekii, Melolontha vulgaris, etc. In Carabus violascens were detected on the maxillary palpi large, plainly microscopical, white disks, which are surrounded with a great number of extremely small teeth.

Whether the above-described organs on the palpi of beetles should be considered as olfactory or gustatory in their nature can only be determined by means of physiological experiments; they probably receive taste-nerve terminations.

Fig. 279.—Olfactory pits of the antenna of Vespa vulgaris.—After Kraepelin.