io6 



ANNELIDA OR ANNULATA 



Anatomy. — At Its anterior end, Lumbricus terrestris has a pro- 

 boscis-like fleshy lobe called the p7'Ostomium, with a mouth imme- 

 diately behind it on the ventral side. The skin is covered by a 

 transparent cuticle which is slightly iridescent, and is externally 

 marked by annulations representing true segments. All segments 

 except the first and the last have four pairs of setae, two pairs being 

 ventral and two pairs ventro-lateral. (Fig. 45, A and B.) 



From the 31st to the 37th somite, the clitellum is situated. This 

 aids the worms in adhering at mating and furnishes a slimy sub- 



~ ~ — Prostomium 



-A Mouth 



Seta 



A 



B 



Fig. 45. A, ventral view of the first four segments of Lumbricus terrestris, showing 

 rows of setae. B, enlarged seta. (Drawn by W. J. Moore.) 



Stance that hardens into the cocoons In which the eggs are fertilized 

 and develop. The setae of the 26th somite are modified for repro- 

 duction. 



The external openings Include the mouth and anus at opposite 

 ends. There are two nephridiopores for each somite except the first 

 three and the last. The two pairs o{ seminal receptacle openings are 

 found between the ninth and tenth and the tenth and eleventh 

 somites. The two oviducal openings are at the 14th somite. The 

 two vasa deferentia at the 15th somite are readily seen. There are 

 also dorsal pores on the middle line of the back between the rings, 



