8o WORMS, ROTIFERS, LEECHES, POLYZOA 



has had an opportunity of looking through a microscope at a 

 " pond-life " exhibition, for they are very favourite objects with 

 every amateur microscopist. The fixed forms are particularly 

 beautiful, the magnificent Stephanoccrus (the so-called "Crown 

 Animalcule ") and the interesting little Brick-maker (Melicerta 

 ringens], which forms a tube of rounded pellets of its undigested 

 food, being two striking though familiar examples. 



The Gephyrea are a group of marine worms with more or less 

 bolster-shaped bodies rather resembling at first sight the Holo- 

 thuria, and appear to occupy a position near the Annelida, or 

 segmented worms. Their bodies are cylindrical, long, without 

 distinct separation into segments, and without any lateral bristles. 

 They live at varying depths, with their bodies buried in the sand 

 or mud, or hidden under rocks, in the shells of molluscs, or the 

 interstices between corals. Many species have a more or less re- 

 tractile proboscis terminated by the mouth. The sexes are sepa- 

 rate, and the young undergo metamorphoses, the larvae often 

 resembling the rotifera in their circles of cilia. 



The Annelida 1 (or Annulata), or Segmented Worms, are a 

 great assemblage of marine, fresh-water, and terrestrial worms, 

 (including the Earth-worms, the marine Segmented Worms, and 

 the Leeches. All are characterised by the possession of bodies 

 divided into a series of segments or rings, upon which bristles, either 

 on processes called " false-feet " (parapodia) or in depressions in the 

 tissues of the skin, are present ; and internally by a spacious 

 cavity or ccelom between the body-wall and that of the digestive 

 tube. Presenting great differences in structure, the Annulata are 

 divided into two great orders, the Few-bristled Worms (Oligochtzta) 

 and the Many-bristled Worms (Polychceta), and the Leeches or 

 Suctorial Annelida, which form a sub-order to themselves. 



The Few-bristled Worms (Oligochczta) are long worms with 

 segmented bodies, and are dwellers in the earth, in oozy mud, and 

 at the bottom of ponds and streams. Their scanty supply of 

 bristles are never borne on false-feet or parapodia; they have 

 no tentacles, do not pass through a metamorphosis, and are all 

 hermaphrodites (i.e. the same individual possesses both male 

 and female reproductive organs). The Many-bristled Worms 

 are dwellers in the sea ; they all have numerous bristles 



1 From the Latin, annulus, a ring. 



