. A manual of zoology. Zoology. 15S GENERAL PRINCIPLES OF ZOOLOGY that representatives of the most diverse groups take on a reniarkable similarity of appearance and structure, rciilastomum (lig. 113), for example, belongs in the same class with the spiders, the Arachnida, but in external appearance it is entirely unlike them, resembling the tape-worms (fig. 11^). Plence for a long time all entoparasites, on account of their similarity, were united into a single systematic group under the name of 'llelminthes,' comprising members of the Crustacea, worms, and spiders. Only l>y emliryology was

- Image ID: RDHDK3
. A manual of zoology. Zoology. 15S GENERAL PRINCIPLES OF ZOOLOGY that representatives of the most diverse groups take on a reniarkable similarity of appearance and structure, rciilastomum (lig. 113), for example, belongs in the same class with the spiders, the Arachnida, but in external appearance it is entirely unlike them, resembling the tape-worms (fig. 11^). Plence for a long time all entoparasites, on account of their similarity, were united into a single systematic group under the name of 'llelminthes,' comprising members of the Crustacea, worms, and spiders. Only l>y emliryology was
The Book Worm / Alamy Stock Photo
Image ID: RDHDK3
. A manual of zoology. Zoology. 15S GENERAL PRINCIPLES OF ZOOLOGY that representatives of the most diverse groups take on a reniarkable similarity of appearance and structure, rciilastomum (lig. 113), for example, belongs in the same class with the spiders, the Arachnida, but in external appearance it is entirely unlike them, resembling the tape-worms (fig. 11^). Plence for a long time all entoparasites, on account of their similarity, were united into a single systematic group under the name of 'llelminthes,' comprising members of the Crustacea, worms, and spiders. Only l>y emliryology was the unnaturalness of tliis grouping recognized. Entoparasitism therefore is one of the best examples for illustrating co)ivcrgc)it development, i.e., animals of different systematic position acquiring, under similar conditions of life, a great similarity of structure and appearance. Symbiosis.—Less frequent than parasitism is symbiosis, or the association of animals for reciprocal advantages. Social animals frequently not only hold certain animals in bondage, but even seek to protect and serve them; as, for example, certain blind beetles, like Clavigcr or some species of plant-lice, (myrmecophiles) or even ants of other species and genera. But such cases of association correspond in part to the domestication of animals, or to slavery, as carried on by man. The ants keep the plant-lice in order to lick the sweet juice ('honey dew') which is secreted in their honey-tubes; they steal the pupaj of other ants and rear them, to use them later as slaves. This state of things rests, consequently, not upon equal rights, since the one animal, in the present example the ant, brings about the association, while the other is passively led into it. SyiJipliyly is close to true symbiosis. Besides Clavigcr, mentioned abo-\-e, many other insects, mostly beetles, which are cared for by the ants, are found in colonies of ants and termites, since they have a sweet secretion on special bundles o