Translations:Benutzer:Arian/Klett-Mini-Test/503/en

It is the reciprocal relationship to warmth that, in the bodily structure of insects, equalises the one-sidednesses attaching to invertebrates, fish and birds. The three functional domains of head, thorax and metabolism are, in the insect as regards bodily form, as a rule more equally developed, with particular emphasis on the middle member (thorax) — indeed they are in many cases sharply demarcated from one another by incisions (insect from Latin insectum = cut-into). Like all arthropods, the insect has no bony inner skeleton; instead, its threefold form is held together by an outer skeleton, the chitin-armour. The polarity of head pole (caput) and metabolic pole (abdomen) is particularly pronounced. Yet the sensory organisation of the head — with compound and simple eyes, and with palps and antennae (sense of smell and touch) — reaches, mediated by the ventral ganglion system, across into the limbs; in certain species, for instance, onto the forelegs (sense of gravity and vibration, hearing, taste).