68 
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 coeca. 
The nervous system is quite simple, consisting of two 
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. — Ankulata {Leeches, Earth-worms, and Sea- 
worms).^ 
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 GepJiyrea are small groups of 
worms, which are described in the author's larger Zoology. They 
may be omitted in an elementary course for want of space. 
