border of the anterior adductor muscle. The ganglia of the two 

 sides are united by a commisure which passes anterior to the 

 oesophagus. 



2. The Visceral ganglia lie on the ventral side 'of the posterior 

 adductor muscle and may be exposed by separating the united 

 lamellae of the inner gills. The two are connected by a short com- 

 missure with each other and are connected with the cerebral ganglia 

 by connectives that may be traced forward a short distance with- 

 out dissection. A large nerve leaves the posterior end of each 

 ganglion and supplies the posterior margin of the mantle and the 

 siphons. 



3. The Pedal ganglia lie in the substance of the foot, dorsal to 

 the muscular part and in front of a loop of the intestine. With 

 a sharp scalpel make a median section of the foot extending it 

 some distance into the visceral mass ; this will expose these gang- 

 lia. They are connected together by a broad commissure, and with 

 the cerebral ganglia by connectives. 



Draw the nervous system, showing the ganglia, connectives and 

 commissures. 



X. DIGESTIVE SYSTEM. 



1. The mouth lies ventral to the anterior adductor muscle. Is 

 it provided with teeth or any organs of prehension ? AYhat is the 

 nature of the food and how is it brought to the mouth? 



2. The oesophagus leads from the mouth to the stomach, which 

 is an enlarged portion of the digestive tract surrounded by a 

 brownish gland commonly called the "liver". 



3. Following the stomach is a much folded intestine, with walls 

 so thin that it is not practicable to trace it in detail. The hinder 

 portion of the intestine runs through the heart and opens by the 

 anus into the cloacal chamber, ventral to the posterior adductor 

 muscle. The general arrangement of the digestive system is well 

 shown by a median sagittal section of a preserved specimen. 



Draw the alimentary canal. 



XIII. ASTERIAS VULGARIS. (The Starfish). 

 A. EXTERNAL CHARACTERS. 



Examine a specimen and note that : 



1. It consists of radiating arms and a central disk. 



2. That the surface by which the animal clings, the oral surface, 

 is different from the other, aboral surface, and that both surfaces 

 are covered with short spines. 



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