60 THE EARTHWORM. 



will however apply with but slight alterations to any of the 

 others. 



The worm is most conveniently killed by dropping it into 

 chloroform for a few minutes 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. Colour. The earthworm is of a pale pinkish or yellowish 



colour, replaced in front by -a dark purplish brown, 

 which extends a considerable distance backwards as 

 a mid-dorsal stripe. The hinder end is also tinged 

 with brown. The dorsal blood-vessel can be seen 

 through the integument, appearing as a dark-coloured 

 wavy line along the dorsal surface. 



3. The annnli, 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 prostomium, or cephalic lobe, is the rounded lobe 



forming the extreme anterior end of the worm. In 

 Lunibricus it extends backwards on the dorsal surface 

 so as to completely intersect the first annulus and 

 meet the second. In Allolobophor a it extends about 

 halfway through the first annulus. 



5. 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 the year. In other species of earth- 

 worm it occupies other segments. 



