The Probert Encyclopaedia of Nature

ARACHNIDA

Arachnida is a class of arthropods. They are the spiders, scorpions, king- crabs and mites. They have the body divided into a number of segments or somites, some of which have always articulated appendages (limbs, etc). There is often a pair of nervous ganglia in each somite, although in some forms (as spiders) the nervous system becomes modified and concentrated. They are oviparous and somewhat resemble insects, but they have a united head and thorax, and do not undergo a metamorphosis similar to insects. They respire by tracheae, or by pulmonary sacs, or by the skin.
Research Arachnida