A MANUAL OF ZOOLOGY 35 



3. In center of section a large oval body, the buccal 

 mass. 



4. The mouth on the ventral surface, 



5. Small. dorsal beak, dorsal to the mouth. 



6. The large msandlhle and the muscle which moves It. 

 In section through the eyes: 



1. The small oesophagus near the center of the section. 



2. Pedal ganglia on the middle lihe of the body. 



3. Byes on the side of the head. 



4. Anterior chamber of the eyes. The posterior cham- 

 ber. The line between the two. 



5. The cornea. The central opening, the pupil. 



The posterior chamber is filled in the living animal 

 with vitreous humor. 



6. The retina on the' back Of the eye; examined under 

 high power, rods between the lines of pigment will be 

 found. 



7. Layer of cartilage outside of the retina. 



8. Optic ganglion outside of the cartilage. 

 Section posterior to the eyes: 



1. Cerebral ganglia dorsal to the middle line. 



2. Optic ganglia on each side of the. head. 



3. Pedal ganglion on the ventral surface of oesophSr 

 gus 



4. Head cartilage outside of the brain. 



5. Upper end of siphon, ventral to the head. 

 Study a section through the base of the head. 

 Make a d rawing of each section stu t^inrt gg ahpv^; 

 TBS~nvIng animal is a very interesting one to study. 



His motions are quick. He moves in any direction by 

 means of the fin and the siphon. His movements back- 

 ward are exceedingly swift, being brought about by the 

 action of the water as it Is thrown out of the siphon. The 

 blind sacs, spoken of above, act as valves that allow the 

 water to enter the mantle cavity, but as the mantle con- 

 tracts to send the water out they close and the water is 

 iorced out through the siphon in jets. 'He has the power 

 to vary the direction Of the jet by moving the point of the 

 siphon to -various positions; ' ■ 



His color Is constantly changing as explained above; 

 ■ ThR tentacles arein' constant motion, in search of food: 



