LUMBRICUS, 199 



Like all other Annelida^ the eaithworm is piano-sym- 

 metric, though the absence of appendages makes this less 

 evident than in other classes. 



The body is constricted throughout into a series of 



about 150 segments, but there are no annuli. The segments, 



g from about 29 to 35,"^ have a swollen appearance 



„ ^ and a yellowish colour. They form the ditellum. 



The mouth is at the anterior end, overhung by 



a prostomium and bordered by the peristomium. At the 



extreme posterior end is the anus. 



As in the leech, there are neither gills nor appendages. 

 If the body of the worm be drawn through the fingers from 

 tail to head it \yill rasp with some resistance to the fingers. 

 This is due to the presence of minute setce which are found 

 on each segment. The setae are in pairs and are arranged in 

 two ventral and two lateral rows. Each segment, therefore, 

 has eight setae. They naturally project backwards and aid 

 the locomotion of the worm in the same way as the appen- 

 dages of Arenicola, In the mid-dorsal line is a row of median 

 dorsal pores, occurring between each segment from about 

 the 9th backwards and communicating with the coelom. A 

 pair of minute nephridiopores open on the ventral surface 

 of each segment (except the first two), but they are too 

 small to be recognised without the aid of a lens. On the 

 15th segment there is a* pair of ventral openings with tumid 

 lips, the male genital openings, and on the segment (14th) 

 in front are the two female genital apertures. Between seg- 

 ments 9, 10 and II there are the two paired openings of 

 the spermathecce. 



The body is covered by a cuticle with simple ectoderm, 



forming a flexible but firm envelope. Scattered 



throughout the ectoderm are numerous uni- 



men ary. cgji^lar glands, specially abundant in the region 



of the ditellum. 



There are no eyes nor otocysts, but the prostomium has 

 Sensory sense-organs for perception of contact and per- 

 haps of taste. The alimentary canal is exposed 

 by making a median dorsal incision along the body of the 

 worm. The mouth passes into the mM^cyAd^x pharynx^ from 



* There is great variation in the position of the ditellum. 



