BRANCH YERMES: THE IVOR MS 129 



the anterior end of the body is the clitellum, agkrtidular 

 structure which secretes the cases in which the 'eggs are 

 laid. On the ventral surface of the fourteenth and 

 fifteenth segments (in most species) are two pairs of small 

 pores ; two other pairs of small openings (usually difficult 

 to find), one between segments 9 and 10, and one between 

 segments 10 and 11, are present. All these are the 

 external openings of the reproductive organs. 



Make drawings showing the external structure of the 

 earthworm. 



Examine a live specimen placed on moist paper or 

 wood. Note the characteristics of its locomotion, and 

 the movements of its body-parts. How do tfie setae aid 

 in locomotion ? 



Internal structure (figs. 25, 26 and 28). TECHNICAL 



NOTE. With a fine-pointed pair of scissors make a dorsal median 

 incision, not too deep, behind the clitellum and cut forward as far 

 as the first segment. Put the specimen into dissecting-dish, care- 

 fully pin back the edges of the cut and cover with clear water or, 

 better, 50^ alcohol. 



Note the long body-cavity divided by the thin septa 

 which have been torn away for the most part by the 

 pinning process. Note the thin transparent covering of 

 the body, the cuticle. Just beneath this note a less trans- 

 parent layer, the epidermis, and underneath this a layer 

 of muscles. The muscular layer is made up of two 

 clearly recognizable sets, an outer circular layer and an 

 inner longitudinal layer the fibres of which are continuous 

 with the septa. 



Note, as the most conspicuous internal organ, the long 

 alimentary canal, of which a number of distinct parts may 

 be recognized. Most anteriorly is a muscular pJiarynx, 

 which is followed by a narrow oesophagus, leading directly 

 into the thin-walled crop; next comes the muscular 



