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nally by rings which correspond more or less closely with 

 the internal segmentation. The body-wall has layers of 

 muscle ; and the skin (of most Annelids) bears chaetae 

 (bristles) which aid in movement. The main nervous 

 system consists of a ventral nerve cord and a ring round 

 the pharynx. The cord generally has distinct ganglia, 

 and there are two cerebral ganglia on the ring. There is 

 a blood circulation. The coelome, generally extensive, 

 communicates with the outside by paired nephridia. The 

 gonads are developed from the coelome lining. Repro- 

 duction is usually sexual (the sexes are separate in the 

 marine Chaetopoda ; earthworms and leeches are herma- 

 phrodite) ; and the development is either direct (i.e., without 

 a larval stage) or indirect, involving a trochosphere larva. 

 Asexual reproduction by fission and budding also occurs 

 (e.g., Nais, Syllis, Autolytus}. 



CLASS CHAETOPODA. 



Lumbricus (The Earthworm). 

 A Type of Oligochaeta. 



Describe the Alimentary Canal of the Earthworm, and indicate 

 the functions of the various Parts. 



The small oral cavity opens into a wide muscular 

 pharynx which is connected to the body wall by radiating 

 muscles. When these muscles contract, the pharynx dilates 

 and the soil is sucked in. The next part is the narrow 

 gullet or oesophagus, which has on each side three pouch- 

 like calciferous glands ; these probably neutralise the 

 acids of the food (the organic debris in the soil). Behind 

 this is the swollen and thin- walled storing crop ; it is 

 separated by a constriction from the thick- walled muscular 

 gizzard in which the food is ground. The intestine, which 

 extends from the gizzard to the anus, is the digestive and 

 absorptive portion of the gut ; it is a sacculated tube, 

 and its surface is further increased by a deep dorsal fold, 

 the typhlosole. The intestine is covered by a layer of 



