56 THE EARTHWORM 



hot or cold saturated solution of corrosive sublimate ; and the 

 dissection is rendered much easier if the worm be put into 

 spirit for twelve hours or more before dissection. 



I. EXTERNAL CHARACTERS. 



1. Form. The body is cylindrical along the greater part of 



its length, flattened in its hinder part. It is pointed in 

 front, blunt behind, and is thickest about one-third 

 of its length from the anterior end. 



2. The general colour of the animal is pinkish, darker in the 



dorsal and anterior part of the body, paler on the 

 ventral surface and in the hinder part of the body ; 

 and with a dark-coloured band down the middle 

 of the back. The dorsal blood-vessel can be seen 

 through the integument, appearing as a dark-coloured 

 wavy line along the dorsal surface. 



3. The annul! into which the body is divided externally by 



transverse grooves, are larger and more obvious in 

 front than behind. Each annulus corresponds to a 

 segment, and is subdivided by smaller grooves, the 

 number of which varies in different regions of the 

 body, and also on the dorsal and ventral surfaces. 



4. The clitellum, or cingulum, is the thickened integument 



of the dorsal and lateral surfaces of the thirty-second 

 and five following segments, but varies slightly both 

 in position and extent in different specimens and at 

 different times of year. In other species of earthworm 

 it occupies different segments. 



5. The setae are short chitinous bristles implanted in the 



body-wall, and arranged in two double rows along 

 each side of the body, each segment except the first 

 and last bearing four pairs. They are easily felt on 

 drawing the worm through the fingers from tail to 

 head. 



The seta are easily isolated by boiling a bit of a worm in 

 a strong solution of caustic potash : they should then be ivashed 

 and mounted in glycerine, or dried and mounted in balsam. 



