90 



CHAPTER VI. 



WOEMS — Continued. 



CH/ETOPODA and HinUDIKEA. 



Of the segraetited worms two groups are of interest to the 

 agriculturist — namely, (i) the Earthworms {Lurnhricidfp) and 

 Aster-worms [Etirliyti-andie), and (ii) the Leeches (IlirwJtniiJw) : 

 the first are beneficial to the soil ; the second are injurious ; the 

 last harmful to horses. 



Segmented worms have a brain, a circum-aesophageal nerve- 

 ring, a ventral nerve-cord, and a definite vascular system. 

 Generally they are round, but some — such as the Leeches — are 

 flattened ventrally. In form most are cylindrical, with a thick 

 muscular skin. The body is made up of a number of successive 

 segments, constricted off externally. Those segments following 

 the head are similar externally and internally. The tail seg- 

 ments differ, and give origin during the growth of the worm 

 to new segments ai.teriorly. The internal divisions are called 

 ili-fucjiiment.'', and may correspond to the external .'iegmentation, 

 or may equal tliree, four, or five of the external rings. 



These worms are found in all manner of places. The Cliceto- 

 poda are marine and terrestrial. The marine species live in the 

 sand, on rocks, shells, \'c. The terrestrial live in damp earth, 

 and others live in fresh water. They all require damp media to 

 flourish in. Very few are parasitic ; those that are so are mainly 

 parasites of plant roots. 



