58 ZOOLOGY. 



Class VI. — Nemertika (Nemertean Worms). 



General Characters of Nemerteans. — The Nemertean 

 worms occur abundantly under stones, etc., between tide- 

 marks and below low- water mark; they are of various col- 

 ors, dull red, dull green and yellowish, and are distinguished 

 by the soft, very extensile, more or less flattened, long and 

 slender body, which is soft and ciliated over the surface, 

 the skin being thick and glandular. 



The mouth forms a small slit on the ventral surface im- 

 mediately behind the aperture for the exit of a large pro- 

 boscis. The oesophagus leads to a large digestive tract, 

 which often has short lateral pouches or cceca. 



The nervous system is quite simple, consisting of twc 

 ganglia in the head united by a double commissure; from 

 each ganglion a thread composed of nerve-fibres and gan- 

 glion-cells passes back to the end of the body. 



Class VII. — Annulata (Leeches, Eartli-worms, and Sea- 



ivorms).* 



General Characters of the Annulates. — This group, rep- 

 resented by the leeches, earth-worms, and nereids or bris- 

 tled sea-worms, tops the series of the classes of worms. 

 With their regularly segmented bodies, their eyes and ears 

 and complicated appendages, they stand nearer the Crus- 

 tacea and Insects than any other class of invertebrate ani- 

 mals, their internal anatomy on the whole being nearly or 

 quite as complicated. 



* Class Enteropneusta and Class Gephyrea are small groups of 

 worms, which are described in the author's larger Zoology. They 

 may be omitted iu an elementary course for want of space. 



