Again, the well-known action of earthworms may be said to be a biological work; but the resulting aeration of the soil causes edaphic differences; and earthworms are absent from certain soils, such as peat.
Various species among those that are predaceous attack smaller insects, hunt in packs crustaceans larger than themselves, insert their narrow heads into snail-shells to pick out and devour the occupants, or pursue slugs and earthworms underground.
Many of our native species spend the day lurking beneath stones, and sally forth at night in pursuit of their prey, which consistsof small insects, earthworms and snails.
They are disposed in two groups on either side, corresponding in the Polychaeta to the parapodia; the two bundles are commonly reduced among the earthworms to two pairs of setae or even to a single seta.
In the earthworms, on the other hand, this coat is thick and composed of many layers.
In the earthworms, on the other hand, the epidermis becomes specialized into several layers of cells, all of which are glandular.
The prevalent number of testes is one pair in the aquatic genera and two pairs in earthworms. But there are exceptions; thus a species of Lamprodrilus has four pairs of testes.
The segments occupied by the gonads are fixed, and are for earthworms invariably X, XI.
Among the aquatic Oligochaeta and many earthworms (the families Lumbricidae, Geoscolicidae and a few other genera) the spermathecae are simple structures, as has been described.
12 and 13 are shown the spermathecae of the genera Hyperiodrilus and Heliodrilus, which are simple sacs ending blindly as in other earthworms, but of which there is only one median opening in the thirteenth segment or in the eleventh.
- Earthworms, rarely aquatic in habit.
Earthworms are divided into the following families, viz.
These ducts therefore have not their exact counterparts in the Oligochaeta, unless we are to assume that they collectively are represented by the seminal vesicles of earthworms and the vasa deferentia.
There are few earthworms or snails.
In that country, also, the earthworms of Europe are noticed to replace native forms as the ground is broken.
The word was introduced to English readers in a translation (1601) of Pliny's Natural History by Philemon Holland, who defined "insects" as "little vermine or smal creatures which have (as it were) a cut or division betwene their heads and bodies, as pismires, flies, grashoppers, under which are comprehended earthworms, caterpilers, &c."
Aldrovandi in De animalibus insectis (1602) almost contemporaneously distinguished between "terrestrial insects," including woodlice, earthworms and slugs, and "aquatic insects," comprising annelids and starfishes.
All reptiles belong to the class of insects, for the same reasons that earthworms belong to it."
The general practice for many years past among naturalists has been to restrict the terms "Insecta" and "insect" to the class of Arthropods with three pairs of legs in the adult condition: bees, flies, moths, bugs, grasshoppers, springtails are "insects," but not spiders, centipedes nor crabs, far less earthworms, and still less slugs, starfishes or coral polyps.
As pairs in each ring-like segment or somite of the body, and some of these are in all cases retained as gonoducts and often as renal excretory organs (green glands, coxal glands of Arachnida, not crural glands, which are epidermal in origin); but true nephridia, genetically identical with the nephridia of earthworms, do not occur (on the subject of coelom, coelomoducts and nephridia, see the introductory chapter of part ii.