THE EARTH WORM 



225 



limbs, but by the segments, assisted or not by lateral projections and cilia. Although there is great 

 diversity in form, the organs and structures of the body are, to a large extent, the same on both 

 sides, and hence there is bilateral symmetry. 



The Vermes are divided into five classes the Annelida, the Gephyrea, the Rotifera, the 

 Nemathelmintha, and the Plathelmintha or the True-ringed Worms, the Marine Worms, the Wheel 

 Animalcules, the Ribbon Worms, and the Flat Worms. 



CLASS ANNELIDA (THE RINGED WORMS). 



SUB-CLASS CH^ETOPODA. 



These Worms have bristles upon the segments, either on processes called false feet (parapodia), 

 or in depressions in the tissues of the skin. Presenting great differences in structure, they are 

 divided into two large ordei's, in one of which (the Oligochaeta) the bristles are comparatively few., 

 and never on parapodia : there are no tentacles, cirri, or branchia3, and the sexes are combined ; these 

 Worms, moreover, do not undergo metamorphosis. The second order (the Polychaeta) are Marine 

 Worms, with separate sexes, undergoing metamorphosis, and they have numerous bristles carried on 

 parapodia, and also tentacles, cirri, and branchiae. 



ORDER OLIGOCH^TA. 



These are long Worms found in eai-th, mud, and fresh water, which are known by their negative, 

 rather than by their positive zoological characters. They have no structures on the sides which may 

 be called "feet," and they have not any armature like jaws, in relation to the pharynx. They are 

 without tentacles, and do not possess cirri or branchiae. The sexes are combined, and there is 

 no metamorphosis. Being Annelida, they have segments, and there are bristles projecting from them. 

 There are two sub-orders of these sparely-bristled Worms, 

 and in the first (the Terrestrial, or Oligochceta terricola) 

 the Earth Worm is the type. 



The Earth Worm, or Dew Worm,* is such a familiar 

 object that it is only necessary to remark on some of its 

 peculiarities. The head is a long, obtuse cone ; the first 

 segment is usually lobe-like ; it overhangs the wide 

 circular mouth, and is more or less retractile within the 

 second ring. The segments of the body are narrow, and 

 furnished with minute bristles, some of which, more or 

 less hooked, are called spinets, and are retractile. There 

 are no eyes, jaws, or branchiae. On the segment behind 

 the first are two furrows, often joined by a cross one; 

 and farther back is a smooth, glistening brown part, 

 differing from the rest of the Worm in appearance : it 

 is called the clitellus. The hinder part of the body is 

 flatter and broadens out, and the anal segment is small, 

 reddish, and has tumid projections. The genital pores 

 are on the fifteenth ring. There may be from twenty- 

 eight to thirty-two rings in front of the clitellus, which 

 has six segments, and 106 behind it. In the skin and 

 clitellus are organs for producing mucus, and it can be 

 noticed that a red fluid circulates in an imperfect circulating vessel called the pseudo-haemal system. 

 The nervous system consists of central ganglia above the pharynx, cords connecting them around 

 the pharynx with a long chain of nerves and ganglia, extending through the length of the body on 

 the ventral wall of that cavity which environs the internal organs the perivisceral. 



The upper lip is slightly elongate, and covers the mouth, which leads to a muscular pharynx, 

 ending within the body, at about the seventh segment ; a narrow oesophagus is continued backwai'ds 

 to about the sixteenth. There are three pairs of pouches in the sides of the resophagus, which contain 



* Lumbricus terrcstris. 

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EAllTH WOKM. 



