PRINCIPLES OF ANIMAL BIOLOGY 65 



2p. Examine (demonstration) contents of the anterior part of the 

 digestive tract. Can you recognize any of the organisms 

 observed in 20? Approximately what proportion of the con- 

 tents is composed of organisms ? If other materials are present, 

 what are they and what is their source? By what means 

 are the food particles brought to the mouth? 



3. The mussel must maintain an upright position by means of the foot, 

 and have its siphonal openings uncovered in order to breathe and feed. 

 On what kind of a bottom would it thrive best? Why is it not found 

 on the ooze bottom in deep water far from shore? Why does it not occur 

 on a solid, clean swept rock bottom? What other animals must live in 

 the same body of water with it? In short, in what situations would you 

 be most likely to find fresh- water mussels and why? 



(6) The Nymph of a Gomphine Dragon-fly (Gomphus). 



1. Examine living specimens in a dish of water on sand bottom. 

 Note: 



la. The tube-like tip of the abdomen with its open end thrust 

 up through the sand. Water enters this opening (anus) 

 to reach the gills which are contained in a rectal respiratory 

 chamber. The opening is guarded by an elaborate strainer. 



Ib. That the animal burrows through the sand when disturbed. 

 Note if possible the method of burrowing. 



2. Examine a specimen in a watch glass of water under a dissecting 

 microscope and note: 



2a. The large grasping labium or lower lip with its hooks and 

 spines. This is hinged so that it may be extended forward 

 far beyond the head, and is capable of being thrust forward 

 and withdrawn with great rapidity. Pull it forward with 

 forceps. The animal is carnivorous and predatory. 



26. The adaptations for digging: 



1. The flattened head. 



2. The flattened fore legs thrust forward. 



3. The remaining legs pressed against the side of the body 

 where they are out of the way; the hind pair extended back- 

 ward against the side of the abdomen. 



3. How does the form of the head and legs, and the structure of the 

 respiratory organs adapt the animal to burrowing in the soft bottom? 



B. ANIMAL REACTIONS 



Of importance in determining the habitat of animals is the manner in 

 which they react to different factors in their environment. A few reactions 

 will be observed here. 



1. Place a number of living planarians (Planaria sp.) in each of several 



