168 THE BIOLOGY OF THE ANIMAL 



dropping out of the mouth again when the next 

 mouthful is swallowed ? Do you find any struct- 

 ures whose function may be to separate the larger, 

 undigested particles of food and prevent their en- 

 trance into the intestine ? 



Are the lobster and the crayfish structurally 

 adapted to capture living animals for food ? Is 

 either adapted for catching as pre}' animals hav- 

 ing quick, active movements ? 



If living specimens cannot be obtained, examine 

 the contents of the stomachs of dead ones. 



c. Breathing. — Place the animal in a dish of water and 

 allow it to become quiet. Then with a pipette run 

 into the water, close to the bases of the hinder 

 thoracic appendages, a few drops of water con- 

 taining particles of indigo, carmine, or India ink. 

 Note the direction of the current. Do the parti- 

 cles enter the branchial chamber ? If so, at what 

 place ? Where do they come out ? To discover 

 the cause of this current, with a pair of strong 

 scissors open the cervical canal by making two 

 cuts : the first directly behind the cervical groove, 

 the second about a half -inch in the lobster, or 

 one-fourth inch in the crayfish, back of the first 

 and parallel to it. Then remove that part of the 

 branchiostegite included between the cuts. This 

 operation can be done with little or no incon- 

 venience to the animal, and permits the action of 

 the scaphognathite to be seen. "Watch the mo- 

 tions of the last. How does it cause a flow of 

 water over the gills? Examine a specimen in 

 which the legs are still attached to the thorax. 

 Move one of the legs. Does the gill or podo- 



