j5^^ earthworms, phylum ANNELIDA 



of the chc-Eta of the twenty-sixth segment during coition, and of the 

 other straight chietae during the formation of the cocoon in which 

 the eggs are laid. 



EXTERNAL OPENINGS 



A number of internal organs open separately upon the surface 

 of the body. We have already mentioned the mouth and anus. 

 The openings of the vasa deferentia are a pair of slits with swollen 

 lips found on the under side of the body in segment 15. In front of 

 them, in somite 14, are the two small openings of the oviducts. 

 The spermathecal pores are two pairs of small, round openings 

 in the grooves between segments 9-10 and lo-ii at the level 

 of the lateral chaetae, but Allolobophora may have three pairs. 

 The nephridiopores are openings which lead from the excretory 

 tubes or nephridia. They are found, as a pair of minute pores 

 in front of the ventral chaetse, in each somite except the tirst 

 three and the last. The dorsal pores are small, round openings 

 on the mid-dorsal line in the grooves between the segments. The 

 first is behind the eighth segment, and there is one in each subse- 

 quent groove. They open into the body cavity, the fluid in which 

 oozes out through them and moistens the surface of the body, 

 mingling with the slime secreted by the unicellular glands of 

 the skin. As this fluid contains amoeboid cells which attack 

 bacteria and other small parasites, it is a valuable defence to 

 the worm against such enemies, which are numerous in the soil. 



BODY-WALL 



The body of the worm may be said to consist of two tubes, 

 one within the other (Fig. iii). The inner tube is the gut, the 

 outer the body-wall. Between the two lies the coelom or body 

 cavity, divided into compartments by a series of septa, which 

 reach from the gut to the body-wall, where they are attached 

 opposite the grooves on the surface of the body. The compartments 

 communicate by numerous openings in the septa. The coelom 

 contains a fluid, and in this float the leucocytes already mentioned, 

 by which small parasites are surrounded and destroyed, both 

 within and without the body. The body-wall is covered by a 

 cuticle. Under this lies the epidermis, an epithelium consisting 

 of columnar cells, many of which are glandular or sensory, with 

 small cells between their bases. The cuticle is composed of 

 hardened protein and is perforated by a pore above each gland 



