218 



ZOOLOGY. 



(b) Circulatory system: A living or newly-killed specimen is some- 

 what better for this. Discover, if possible : 



Dorsal vessel (just dorsal to the digestive tract). 



Ventral vessel (just ventral to the digestive tract). 



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 contents of the blood vessels with the microscope. 



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

 for satisfactory results in an elementary class. Instead of a detailed ex- 

 amination note the reproductive segments (in the region of the oesophagus) 

 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.) 



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

 Brain, two whitish ganglia just dorsal to, and in front of the pharynx : 

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

 the first of a double longitudinal chain of ganglia which give off 

 nerves in each segment. How are the ganglia of the ventral chain 

 related to the dissepiments? 



(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, 264). How many in each segment? 

 . 5. Microscopic Demonstration. The teacher should make or secure 

 good permanent mounts of transverse sections of the earthworm, by means 

 of which the students should make out the following points. (See Fig. 101.) 

 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. 



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

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

 plement 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 



