Page:Popular Science Monthly Volume 39.djvu/246

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234
THE POPULAR SCIENCE MONTHLY.

all the chatoyant dust, and to lay bare the transparent membrane which it covered.

Some Coleoptera, as the Larinus and the Polydrosus, become unrecognizable when an awkward hand has stripped them of their magnificent raiment; the emerald robe and the curious designs disappear, to give place to the dark coloring of the teguments.

PSM V39 D246 Circulatory apparatus of the cockchafer.jpg
Fig. 15. Circulatory Apparatus of the Cockchafer. a o, aorta: c, dorsal vessel; m, suspensory ligaments of the wings (Straus-Durckheim. Anatomie comparée des animaux articulés.)

The circulatory apparatus of insects (Fig. 15) comprises a dorsal vessel (or heart), from which the ramifications start that distribute the life-giving fluid through the organization. The nervous network (Fig. 16) extends over the ventral face of the animal in the shape of two ganglionic cords which come together under the digestive tube to separate again into two branches. The latter embrace the œsophagus like a collar, and meet above it to inclose the cerebral mass.

As we have just seen, the nervous system is specially localized in the ventral region, while the seat of the circulatory apparatus is chiefly in the dorsal region. This is almost the exact contrary of what is remarked in vertebrates.

The digestive apparatus (Fig. 17) is situated between the circulatory and the nervous networks. The respiratory orifices, which give passage to the air, are distributed along the body. They are called stigmata. Upon them abut the tracheæ, tubes of an extreme tenuity, the interlacings of which branch out through the tissues.

The whole body of the insect is sensitive to touch, but the perception of sensations takes place chiefly by hairs in direct relation with the nervous system. These hairs are found more or less all over the creature, but particularly upon the antennæ and at the ends of the palpi.

The convenient arrangement of the eyes enables the insect to see all around itself without making any motion. The length of its view has not been precisely determined, but experiments seem to show that it is not great. The part played by the ocelli is also not clearly determined. In insects living in dark places, especially in those strangely shaped ones that live in caves, the organ of sight is atrophied, and is represented only by little swellings hav-