These last are again subdivided into the following: The Archiannelida or Primitive Annelids, some of which have a curious ciliated larva, already referred to (p. 42) as the typical Trochosphere or Wheel-ball; the Oligochæta (Few-Bristles), which include the familiar earthworms; and the Polychæta (Many-Bristles). Of the latter, some, the Tubicola, live in tubes which may or may not be fixed to some object; while others, the Errantia, or Wanderers, are free and very active. _Nereis_, the Rainbow Worm (p. 159) may be named as an example. Our illustration shows instances of each group. _A_ is the Sea-Mouse, a bristly creature so named by some very imaginative person. It has two kinds of bristles, long and short, the former being possessed of a peculiar lustre (see p. 73). _C_ is _Syllis_, one of a very curious family of worms. In both _A_ and _C_ are seen a row of paired appendages; these are not "legs," but expansions called "parapodia" which serve the purpose of legs, besides which they frequently act as breathing organs, a special part being appropriated to this purpose. Each of these animals is active and carnivorous, and has a head. The Syllidæ are remarkable for the very peculiar way in which they divide, new individuals being formed and cast off from the end of the body. There is, however, a deep-sea form of _Syllis_ which divides in a very odd manner, giving rise to new individuals placed transversely. The result is a most extraordinary looking creature, a network of worms with numerous heads, each branch being eventually provided with one of its own. [Illustration: FIG. 12.--Worms. _A_, a Sea-Mouse, _Aphrodite aculeata_; _B_, _Terebella littoralis_; _C_, _Syllis_; _D_, _Serpula vermicularis_; _E_, _Spirorbis nautiloides_, on a piece of seaweed.] The tube-dwelling worms are represented in our picture by _Terebella_, _Serpula_ and _Spirorbis_, all very common forms on the English coasts. The _Terebella_ glues around its body a number of grains of sand and bits of shell, thus forming a case; the projecting threads at the head end are the gill-filaments, borne by the anterior segments of the body. These are plumed; the thread-like structures which are seen to lie in front of them are the tentacles or feelers. _D_, _Serpula_, is common on shells and stones. The animal has a plumy bunch of gill-filaments, brilliantly coloured, and a stopper with which it can close the mouth of its tube. This precaution is necessary to keep out its predatory cousins belonging to the Errantia, who poke in their heads and eat the tube-dwelling worms. _E_ is _Spirorbis_, a minute form with a coiled tube, which looks at first sight like a small univalve shell. It is common everywhere, on shells and stones, and encrusting Fuci and other seaweeds, which it sometimes covers almost completely. Spirorbis also has plume-like gills and a stopper. In the latter is a cavity where the creature's eggs are incubated for a time.