It can be demonstrated that insects possess the senses of sight, smell, taste, and touch. The auditory sense is doubtful. Perhaps a sense of touch modified for the perception of delicate vibrations may bear a deceptive resemblance to hearing. A sixth sense has nowhere been shown to occur. A photodermatic sense, modified for light-sensation, must be regarded as a form of the tactile sense. It occurs in many insects. This sense is in no respect of an optic nature. In aquatic insects the olfactory and gustatory senses perhaps grade over into each other somewhat (Nagel), since both perceive chemical substances dissolved in the water. The visual sense of the facetted eyes is especially adapted for seeing movements, i. e., for perceiving relative changes of position in the retinal image. In flight it is able to localise large spatial areas admirably, but must show less definite contours of the objects than our eyes. The compound eye yields only a single upright image (Exner), the clearness of which increases with the number of facets and the convexity of the eye. Exner succeeded in photographing this image in the fire-fly (Lampyris). As the eyes are immovable the sight of resting objects soon disappears so far as the resting insect is concerned. For this reason resting insects are easily captured when very slowly approached. In flight insects orient themselves in space by means of their compound eyes. Odor, when perceived, merely draws these animals in a particular direction. When the compound eyes are covered, all powers of orientation in the air are lost. Many insects can adapt their eyes for the day or night by a shifting of the pigment. Ants see the ultra-violet with their eyes. Honey-bees and humble-bees can distinguish colors, but obviously in other tones than we do, since they cannot be deceived by artificial flowers of the most skilful workmanship. This may be due, to admixtures of the ultra-violet rays which are invisible to our eyes. [Illustration: Fig. _W._] [Illustration: Fig. _F._] [Illustration: Fig. _M._] EXPLANATION OF THE FIGURES. Brain (supra-œsophageal ganglion) of an ant (_Lasius fuliginosus_), magnified 60 diameters, seen from above. Fig. _W._ Brain of the Worker. Fig. _F._ Brain of the Queen (Female) Fig. _M._ Brain of the Male. _St._ = Brain trunk. _L. op._ = Lobus opticus (optic lobe). _L. olf._ = Lobus olfactorius sive antennalis (olfactory lobe). _N._ = Facetted eye. _N. olf._ = Nervus olfactorius sive antennalis (olfactory nerve). _O._ = Ocelli, or simple eyes with their nerves (present only in the male and queen). _H._ = Cellular brain cortex (developed only in the worker and queen). _C. p._ = Corpora pedunculata, or fungiform bodies (developed only in the worker and queen). _R._ = Rudimental cortex of male. The length of the whole ant is: in the worker 4.5 mm; in the queen 6.0 mm; in the male 4.5 mm.