ANNELIDA 2 25 



Hearts, transverse vessels connecting the longitudinal vessels, in segments 

 VII to XI. 



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 gangUa which g^ve off nerves in each seg- 

 ment. How are the ganglia of the ventral cliSin 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. — Good permanent mounts of transverse sections 

 from various regions of the earthworm are valuable. Students should identify 

 the structures studied in the gross dissection, and determine the nature of the 

 following parts (see Pig. 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 waU 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 suppli- 

 ment the students' work on the earthworm. They seem to the 

 author much to be preferred even to the earthworm for an un- 

 derstanding of the arrangement of the internal organs. 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; 



IS, 



