140 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



XV. THE GENERAL ANATOMY OF THE EARTH- 



WORM. 



(Lumbricus.) 



I. EXTERNAL FORM. 



The external characteristics may be studied in an alco- 

 holic specimen, or one which has recently been killed with 

 ether. If alcoholic specimens are used, they should be 

 placed in water for a few hours. The various reproduc- 

 tive apertures are much more conspicuous in some speci- 

 mens than in others, according to the sexual condition of 

 the animal, and if there is difficulty in finding them in one 

 specimen, another may be tried. Their positions vary 

 somewhat, according to the species, and the numbers 

 given here apply to L. terrestris, but any other species 

 will answer for examination. 



In the examination of the external form, notice : 



1. The long, cylindrical body, divided by contrictions 

 into rings, or segments, of which there may be as many as 

 three hundred and fifty. 



2. The anterior end, or that at which the segments are 

 largest. 



3. The brownish-red, slightly iridescent, dorsal surface. 



4. In the median dorsal line, the bright-red, dorsal 

 bloodvessel may be seen through the integument, and in 

 a small, transparent, living animal, irregular pulsations of 

 this vessel can be detected. 



5. The ventral surface is of a much lighter color, and 

 more iridescent than the dorsal. 



6. At a point about one-third the length of the body 

 from the anterior end, notice a thick, glandular white ring 

 or saddle, the girdle, or clitellus, which is formed by the 



