OVARIES AND TESTES. 



143 



6 1 i 'V 



OV- 

 OS 



; 



1H 



TA 





these, LumlyriciiS) like most animals, Las accessory organs of re- 

 production which act as reservoirs or carriers of the germs, assist 

 in securing cross-fertilization, and minister to the wants of the 

 young worms. 



Essential Reproductive Organs. The ovaries are two in num- 

 ber and lie one on either side in the 13th somite attached to 

 the hinder face of the anterior dissepiment (ov, Fig. 80). They 

 are about 2 mm in length, distinctly pear-shaped, and attached by 

 the broader end (Fig. 82). The narrow 

 extremity contains a single row of ova 

 and is called the egg-string (e.s). In this 

 the ova are ripe or nearly so ; behind they 

 shade off into those more and more im- 

 mature till these are lost in a mass of 

 nearly un differentiated cells (primitive 

 ova), constituting the great bulk of the 

 ovary. Each of these, however, is sur- 

 rounded with still smaller cells constitut- 

 ing its nutrient envelope or follicle. As 

 the ova mature the follicles still persist, 

 and they may be detected even in the 

 egg-string. When fully ripe the ovum 

 bursts the follicle and is shed from the 

 end of the egg-string into the body-cavity, 

 where it floats for a time in the coelomic 

 fluid. It is ultimately taken into the 

 oviduct and carried to the exterior. 



The spermaries or testes (t.t, Fig. 80) 

 are six in number, and are perhaps the most conspicuous of all 

 the internal organs of the earthworm. They are large white 

 bodies arranged in three pairs united into one lobed mass which 

 lies between the 10th and 12th somites, and partly covers the 

 oesophagus. Towards the median line they are connected with a 

 large sac (s.v, Fig. 80) underlying the oesophagus. This is the 

 seminal vesicle, a reservoir for the storage of the ripe sperma- 

 tozoa which are produced in the various lobes of the testes. A 

 median partition divides it into a fore part connected with the 

 anterior pair, and a hinder part connected with the middle and 

 posterior pair of testes. These chambers are usually regarded 

 as two separate seminal vesicles, but are often scarcely distinct, 



A 



FIG. 82. The ovary, much en- 

 larged; 6, the basal part; a, 

 body of the ovary containing 

 immature ova; e.s. egg-string; 

 ov, ripe ovum ready to fall off. 



