104 LABORATORY WORK. 



middle, beginning at the free edge and carrying the incision 

 to the end of the body. This lays open the mantle chamber. 

 Lift the cut edges carefully, looking for the median mantle 

 artery running^ f rom the body to the mantle. Pin out the 

 mantle and make out the following points: 



The siphon; notice its inner end; just behind it is the 

 end of the intestine. On either side of the siphon are the 

 siphonal cartilages, grooved on the surface. Look on the 

 edge of the mantle and find a ridge. Close up the mantle 

 and see how the parts interlock. 



Behind the siphon, at either side of the body, are the 

 gills. What structure have they? Can you see any vessels 

 connected with them? Follow the intestine back from 

 the vent. Is it free, or is it tied down to the underlying 

 structures? Notice that it passes across a dark-colored 

 body the ink-sac. Some distance behind the gills see a 

 vessel, the postcava, coming from the side of the mantle 

 forward to the body. 



The other features vary considerably accordingly as the 

 specimen is male or female. In the female the hinder part 

 of the body is occupied with eggs, while upon that part 

 between the gills are the large, transversely striated nida- 

 mental glands* When these are carefully removed the 

 structures are much as in the male. 



On either side of the intestine, a little behind the ink-sac, 

 is the small opening of the kidney; the kidneys themselves 

 stretch back behind the base of the gills. They are irregu- 

 lar in shape. When they are removed f there will be seen 

 in the median line the systemic heart. Behind, it gives 

 off an arterial trunk, which soon divides to form the median 



* These secrete the capsules in which the masses of eggs are laid, 

 f Cut through the thin wall of the kidney just behind the gill, 

 pull off the thin skin, and wash away the granular contents. 



