DISSECTION OF SQUID. 255 



of the alimentary tract and the central part of the nervous 

 system can be easily studied. 



Just inside the mouth, which is placed in the centre of 

 the circle of arms, is the oval buccal mass, which is only 

 slightly connected with the rest of the head. In this find 

 the two horny jaws, black at the tips, and shaped some- 

 thing like the beak of a parrot. Do these jaws work in a 

 vertical or in a horizontal plane? The cavity of the 

 mouth lies inside these jaws and passes nearer to the dorsal 

 jaw. Just inside the mouth-cavity is a pocket given off 

 on the ventral side, in which will be found a horny lingual 

 ribbon, covered with minute horny teeth. Could this 

 ribbon be used in rasping the food after it had passed the 

 jaws ? Notice that the bulk of the buccal mass is made 

 up of muscles arranged to move jaws and lingual ribbon. 



From the buccal mass trace the oesophagus backward to 

 the point where it was left in the previous dissection. Do 

 not cut at first in tracing it, as you would be apt to injure 

 other portions. If the section of the head be in the 

 median plane, the course of the oesophagus will be easily 

 followed without dissection. If not, it can be traced later 

 after the nervous structures have been studied. 



A little back of the buccal mass some harder, cartilage- 

 like structures will be seen in the cut surface of the head. 

 These form a brain capsule, resembling in some respects 

 the vertebrate skull. In the dorsal side of this will be 

 found a large centre, the cerebral ganglion, while on the 

 ventral side two somewhat smaller ganglia occur. The 

 anterior of these is the pedal ganglion, and from it nerves 

 can be traced running into the arms. The posterior is the 

 visceral ganglion. Between the cerebral on the one hand 

 and the pedal and visceral ganglia on the other passes the 

 oesophagus. In one half of the head demonstrate by dis- 



