174 Annelida. 



•chsetae in eaoli bundle. Eyes are absent. Just in front of tlie middle is the 

 -clitellum, a thickened region of skin, covering several segments; and containing 

 a large number of glands, whose mucous secretion holds the individuals together 

 during copulation, and possibly also forms the cocoon in which the eggs are laid. 

 In each cocoon there is generally a large number of eggs. The pharynx is not 

 eversible ; jaws are wanting. Earthwoims of different species live in cultivated 

 soil, in which they burrow, and upon which they feed. They consume dead vege- 

 table matter, also assisting its decomposition by drawing it into their holes and 

 pouring over it a salivary liquid. The excreta are deposited for the most part at 

 the surface, whither the animal usually repaii-s only at night. In severe cold, as 

 in very great heat, the worm leaves the surface soil, and goes into the substrata ; 

 here the holes are long, usually pei-pendicular, and lined with an excreted 

 substance. There is generally an expansion at the bottom, where the animal 

 lies in a drowsy condition, as much as 2 to 3 m. below the gi-ound. By these 

 habits, especially by devouring soil and replacing it on the sui-face in the form of 

 excreta, the Earthworm does moi-e than any other animal to promote the natural 

 ■elaboration of the soil, and attains thereby a paramount importance in the economy 

 oi nature. "When a place is deserted by Earthworms on account, e.g., of an 

 inadequate supply of moistui'e, the surface soil changes and assumes a dry turfy 

 •character; should this occur in a forest, natural planting, by self -sowing, ceases, 

 .and unless man interfere, the wood gradually becomes a moor. 



2. The Na'idx (Nais) are small (seldom more than 1 c/m. long), thin, and 

 transparent ; there are usually two eyes on the prostomium. The chaetse of the 

 dorsal bundle are long and haii'-like, those of the ventral bundle short and hooked. 

 Asexual reproduction is of frequent occurrence. The Naidse live amongst 

 the vegetation in fresh water. Tuhifex rivulorwm, a reddish worm, common in 

 fresh water, is related to Nais. It forms bvuTows in the mud, from which, so 

 long as it is undistiirbed, the hinder part of its body protrudes in constant 

 motion. Often many specimens are found close together, so that the surface of 

 the mud seems to be coloured red in places ; at the slightest movement of the 

 water, the animals withdraw, and the red colom* vanishes. ' 



Under the term Gephyrea is usually included a number of vermiform 

 animals, regarded as constituting a special class of the Annelids. When some 

 forms which have proved to be Molluscs, have been removed from the group, the 

 remainder are evidently aberrant, peculiarly modified, Ohaetopods. 

 Some still possess c h a e t se similar to those of the Chsetopods, but in small 

 numbers, and not arranged in bundles. External segmentation is in- 

 variably wanting ; instead of the double ventral ganglion chain, there is a single 

 stout nerve cord without ganglionic swellings ; it splits anteriorly into two 

 •cords encircling the buccal-cavity, and uniting with the often very slightly 

 developed cerebral ganglion. The nephridia are very large, but few in 

 number, at most three pairs, often only one pair, or a single one. They serve 

 as efferent ducts for the genital products which are formed on the walls of the 

 body-cavity. The sexes ai-e separate ; a metamorphosis oocui-s similar to 

 that of the typical Chsetopod. It is significant that at an eai-ly stage, segmen- 

 tation of the body is sometimes indicated. Their habits resemble those of the 

 majority of Chsetopoda ; they are all marine. An interesting foiin, Bonellia 

 viridis, occurs in various European seas [e.g., the Mediterranean) ; the female 

 possesses at the front end of the short saccular body, a very long tentacle-like 

 prostomium, whose anterior end is forked (body, 6 c/m. ; prostomium, 1 — 2 m.) ; 

 only two chEetsB are present, and one segmental organ. The pigmy male is 

 •quite differently proportioned ; it is 1 — 2 m/m. long, and like a TurbeUarian, 

 uniformly ciliated, with neither mouth nor anus, and without prostomium ; it 

 lives in the nephridium of the female. 



