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TTTKI 

 ANNUL O S A. 



CHAPTER XXIII. 



i. GENERAL CHARACTERS OF THE ANNULOSA. 2. DIVISIONS 

 OF ANNULOSA* 3. GENERAL CHARACTERS OF THE Sco- 

 LECIDA. 4. CHARACTERS OF THE T^NIADA. 



SUB-KINGDOM ANNULOSA. The Annulose animals are charac- 

 terised by the possession of a body which is usually more or less 

 elongated, and is always bilaterally symmetrical, instead of being 

 radially disposed. Very commonly the body is divided into similar 

 (homonomous) segments, which may be definite or indefinite, and 

 are arranged along an antero-posterior axis. Lateral appendages 

 may be absent or present, and when present, are symmetrically 

 disposed. A nervous system is present, and consists of one or two 

 ganglia placed in the anterior part of the body, or of a ventr ally- 

 placed double gangliated chain, 



The association of the Scolecida with the normal Annulose 

 animals renders necessary an exceedingly general, and there- 

 fore correspondingly vague, definition of the sub -kingdom 

 Annulosa. The sub-kingdom may, however, be divided into 

 the following three primary sections, each of which admits of 

 being characterised in a sufficiently definite manner : 



I. Scolecida. This division includes the parasitic worms 

 (Entozoa), the Wheel-animalcules, and some allied forms, and 

 is characterised by having an elongated or a flattened body, 

 which may have an annulated integument, but which is not 

 at all, or but imperfectly segmented. . A water-vascular system 

 is present, but is not concerned with locomotion. There is no 

 true blood-vascular system, and the nervous system consists 

 of one or two cephalic ganglia, and never has the form of 

 a gangliated ventral chain. Lateral appendages are almost 

 universally wanting. 



The Scolecida were formerly placed by Huxley along with 

 the Echinodermata in a special sub-kingdom (Annuloidd) ; and 



