128 INVERTEBRATE ANIMALS. 
SUB-KINGDOM IV. ANNULOSA. 
CHAPTER XII. 
ANARTHROPODA. 
SUB - KINGDOM ANNULOSA.— In this sub-kingdom are com- 
prised an enormous number of animals which agree in the 
following characters (fig. 56). The body is composed of a 
number of segments or rings arranged along a longitudinal 
axis. There is a distinct alimentary canal (0), placed cen- 
trally as compared with the other organic systems, and com- 
pletely shut off from the general cavity of the body. The 
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(ibe TOY 
ae 
a 
Srekele yo 
Fig. 56.—Diagram of an Annulose animal. a@ Blood-vascular or hzmal system ; 
& Digestive system ; ¢ Neural system. 
hemal or blood-vascular system may be absent, but, when 
present, it is always situated on the dorsal aspect of the body 
(a). The nervous system is always present, and is placed along 
the ventral surface of the body. In its typical form it consists 
of two nervous cords running along the whole length of the 
ventral surface, and having a pair of ganglia developed in each 
ring. The first pair of ganglia is always placed above the 
gullet, and the second below, so that the gullet is surrounded 
by the two cords uniting these ganglia (constituting the so- 
called wsophageal collar). The limbs (when present) are al- 
ways turned towards the neural aspect—that is to say, towards 
that side of the body upon which the nervous system is situated. 
