168 THE BIOLOGY OF AN ANIMAL. 



actual evolution. Before entering upon this study, however, it 

 is desirable to take a preliminary survey of the different kinds 

 of living things by a brief consideration of the outlines of zoo- 

 logical and botanical classification. 



PEACTICAL STUDY OF LUHBRICUS. 



A. General External Characters. 



Observe in well-preserved specimens the general form, the 

 somites (count), clitell um, anterior and posterior ends, mouth and 

 anus, right and left sides, dorsal and ventral aspects, number and 

 arrangement of the setae. Compare the prostomium with the first 

 somite, and the different somites with one another. 



B. Openings. 



With a hand-lens observe in a large specimen the openings of 

 a. Sperm-ducts (15th somite). 

 I. Oviducts (14th somite). 



c. Seminal receptacles (9-10, 10-11 somites) (difficult). 



d. Pores into the coelom one in the middle line of the 



dorsal aspect of each somite. 



e. (? Nephridia, very difficult to see.) 



C. Living Earthworms. 



1. Place large, active worms on a moist, rough surface (a wet 

 hoard will answer), and study carefully the mode of locomotion. 

 The direction of crawling is normally forwards, but often back- 

 wards if the anterior extremity be cautiously touched. 



2. Note the quick reflex actions called forth by stimuli (taps, 

 etc.). 



3. Place a worm on its back and note the results. 



4. Place a worm under a bell-jar with a small open dish of 

 chloroform. Note 



a. Speedy loss of sensibility to stimuli. 



1. Afterwards, pronounced rigor mortis (p. 46). 



c. Place a chloroformed worm (not in rigor] in water and 



gradually heat to about 50 C. Note the rigor ca- 



loris. Compare with rigor mortis. 



5. Note in a fresh worm the pulsations of the dorsal vessel 

 seen through the skin. 



6. Place worms in a large, covered, shallow dish, with bits of 



