MAKING MOLLUSCS 197 



After noting the nature and position of the one or two adductor 

 muscles previously cut through, we turn the upper mantle lobe 

 upwards, laying it back over the hinge of the shell, cutting it 

 through at the bases of the siphons if we find it is united with the 

 opposite lobe at those points ; or, if not united, we observe two points 

 at which the lobes touch each other in order to form the siphonal 

 openings. 



Several organs are now exposed to view. The lower mantle 

 lobe is seen in close contact with the valve below it, and if we touch 

 its edge we shall probably observe that it is retracted slightly by the 

 contraction of its own muscular fibres. The tip of the foot is also 

 seen projecting towards the anterior end, its base being hidden 

 between the two sets of plate-like gills that extend along the length 

 of the body. On touching the tip of the foot we find it retract by 

 the contraction of the muscular fibres of which it is composed, 

 aided, perhaps, by the action of one or more retractor pedis muscles 

 with which it is supplied. On raising the upper gill-plates we may 

 observe the dark colour of the digestive gland (liver) at the base of 

 the foot, and also see two or more tentacles or labial palpi on the 

 anterior side of the same. 



Between the labial palpi is the mouth, which leads into the 

 stomach by a short, wide tube, and then into a convoluted tube 

 which finally passes through the heart, and terminates near the 

 exhalent siphon as above described. The whole length of this tube 

 may be followed by careful dissection, its direction being determined 

 at short intervals by probing it with a bristle that has been tipped 

 with a little melted sealing wax. It will be seen to wind through 

 the base of the foot, surrounded through the greater part of its 

 course by the digestive gland, from which a digestive fluid enters it 

 through small ducts. 



The diagram on p. 194 shows the general internal anatomy of 

 a lamelh'branch, parts of which have been removed to reveal the 

 underlying structures. The animal lies in its left valve, the right 

 valve, the right mantle lobe, and the right set of gill-plates having 

 been completely dissected away. The whole course of the digestive 

 tube has also been exposed, and the positions of the three nerve 

 ganglia, with their connecting nerve cords, constituting the central 

 portion of the nervous system, are also indicated. 



It will be interesting, finally, to learn the direction taken by the 

 water currents which supply the animal with air and food in their 

 course through the system. Passing in through the inhalent siphon, 



