CLASS VI. ANNELIDA. 615 
he lias seen the revival of one of these little creatures, on being put in water, after having been 
four years thus completely desiccated ! These animals comprise two orders, the Natantia and 
the Sessilia. 
ORDER 1. NATANTIA. 
This term means swimming, and is apphed to those species of the class which are free and 
swim about from place to place. These have a sucker-like organ, or a small pair of forceps, at 
the tail, by which they are enabled to fix themselves when they wish to set their wheels in mo- 
tion, in order to obtain food. They are divided into two families, the Polytrocha and the Zygo- 
troclia. 
ORDx^.R 2. SESSILIA. 
This term means sitting, and is applied to those species of the class which remain fixed and 
stationary. They include two families, the Floscularidce and the Megalotrochidm. 
THE LOB-WOEM. 
Class VI. AT¥WEr.II>A. 
In the Annelida, which include the Red-blooded Worms, the division of the body into seg- 
ments is usually distinctly recognizable ; the majority live in water, or in damp situations ; a very 
few only are parasitic in their habits. In most the head is distinctly marked, and furnished with, 
organs of sense, such as eyes, tentacles, and in some instances auditory vesicles. The nervous 
system, in the higher forms, exhibits the articulate type of structure very distinctly ; it usually 
consists of a series of ganglia running along the ventral portion. The digestive apparatus con- 
sists of a straight intestine, running through the body from one extremity to the other. The 
mouth is usually armed with jaws, and the opposite extremity of the intestinal canal always ter- 
minates in an anal opening. The sexes are usually distinct, although a few, as the leeches and 
earth-worms, are hermaphrodites. Some species appear to propagate by spontaneous division, 
and many of them can reproduce parts lost by accidental injury. These animals include four 
orders, the Errantia, Tuhicola, Scolecina, and Suctoria. 
