304 PECTIN ARIA. ORDER TERRICOLA. 



and they carry these about with them, when roaming in search of 

 food. It is perhaps in consequence of their locomotive powers, 

 which give them a greater facility of selection, that they construct 

 their shelly tubes with so much more regularity than other 

 Annelidans. These tubes, usually about two inches long, may 

 be frequently picked up on our shores. Some of this group, 

 however, are fixed like the other Tubicola, and form their tubes 

 less regularly. Their bodies are doubled up, as it were, within 

 these envelopes ; so that the intestine terminates in a tube which 

 is curved back over the head. The young of these creatures, 

 when just hatched, are all active, ciliated animalcules, furnished 

 with eyes, which they lose on approaching maturity. 



ORDER III. TERRICOLA. 



913. The Annelida of this Order have a cylindrical body, 

 tapering to a point at its extremities, and furnished only with 

 several rows of bristles ; these are frequently invisible to the 

 naked eye, but may be distinguished by the resistance they make 

 when the finger is passed along the body from behind forwards, 

 their points being directed backwards, in order to give the 

 animal a firm hold of the earth through which it is boring. The 

 head of tnese animals is not distinct from the body ; and they 

 have neither eyes, antennae, mandibles, cirrhi, nor external gills. 

 Their bodies, however, are distinctly divided into segments ; and 

 these are marked by minute spots on each side (Fig. 632, a\ 

 which are apertures leading to small respiratory sacs, on the 

 walls of which the blood is submitted for aeration to the air or 

 water received into them. This Order includes only two princi- 

 pal groups, the Earth- Worms and the JVaids, the former be- 

 ing inhabitants of the land, and the latter of the water. 



914. The Earth- Worms, which nearly all belong to the genus 

 Lumbricus, generally live beneath the surface of the ground. In 

 boring, the Worm insinuates its pointed head between the par- 

 ticles of the earth, penetrating like a wedge ; and in this 

 position, the anterior part of the body is fixed by the spines or 



