224 ZOOLOGY 



Hearts, transverse vessels connecting the longitudinal vessels, in segments 

 VII to XL 



There are other vessels more difficult to find. Examine a drop of the con- 

 tents of the blood vessels with the microscope. 



(c) Reproductive System: These organs are rather too complicated for satis- 

 factory results in an elementary class. Instead of a detailed examination note the 

 reproductive segments (in the region of the esophagus) with the whitish bodies 

 showing at the sides of the alimentary canal, and ventral to it. They are attached 

 to the septa. (Compare figures in various text-books.) Make a composite dia- 

 gram of your own. 



(d) Nervous System: In a well-hardened preparation, identify: 



Brain, a whitish lobed ganglion just dorsal to, and in front of the pharynx; 

 collar, around the mouth, connecting the brain with ventral ganglia, the 

 first of a longitudinal chain of ganglia which give off nerves in each seg- 

 ment. How are the ganglia of the ventral chain related to the dissepi- 

 ments ? 



(e) Excretory Organs: Just lateral to the nerve-chain the student may be 

 able to find coiled thread-like structures (nephridial tubes) in nearly all the body 

 segments (see text, 270). How many in each segment? 



5. Microscopic Demonstration. The teacher should make or secure good, per- 

 manent mounts of transverse sections of the earthworm, by means of which the 

 students should identify the structures studied in the gross dissection, and make 

 out more exactly the nature of the following parts (see Fig. 103) : 



Cuticle, or outer layer. 



Body wall, and the relation of the circular and longitudinal muscles. 



The ventral nerve-chain in position. 



The dorsal and ventral blood vessels. 



The wall of the digestive tract; gland cells, typhlosole, etc. 



259. Dero (or other minute aquatic Annelid). Any one of 

 these fresh -water worms may be used very profitably to sup- 

 pliment the students' work on the earthworm. Mount the 

 living worm, being careful to support the cover-glass. Study 

 with low power. Compare at all points with the earthworm. 

 Dero may usually be had at any season of the year by taking 

 mud and organic matter from the bottoms of foul brooks or 

 ponds and placing it in vessels in the laboratory. The worms 

 will usually come to the sides of the vessels where they may be 

 seen. Owing to its transparent qualities, such a form will be 

 especially valuable in giving the student a better idea of the 

 performance of function in the group. What evidences of mus- 

 cular action are manifest ? How is locomotion effected ? Posi- 

 tion and mode of action of setae? Study the capture of food; 

 how is its progress through the digestive tract, and its elimina- 

 tion therefrom effected? Do you discover any circulation of 



