THE PHYLUM ANNELIDA 



The male efferent ducts bee^in within the seminal vesicles as two pairs of fluted 

 funnels, one funnel lying posterior to each testis. From each funnel, a ductus 

 eflferens (vas efferens) passes through the wall of the vesicle; the two ductus 

 efferentes on each side unite in the coelom to form a ductus deferens, which 

 passes through the body wall in segment 15 and opens externally in a male 

 genital pore. The final items in this complex reproductive system arc two 

 pairs of seminal receptacles. These are sac-like structures protruding into the 

 coelom in segments 9 and 10, opening only on the outer surface of the worm. 

 Their function is to receive spermatozoa from another individual during 

 copulation and to retain these spermatozoa until the subsequent time of 

 fertilization of the eggs. The system is so arranged that only spermatozoa 

 from the seminal receptacles can fertilize the eggs of the individual to which 

 the receptacles belong, thus insuring cross-fertilization. 



During copulation, spermatozoa accumulated in the seminal vesicles of each 

 worm are transferred to the seminal receptacles of its partner, passing by 

 way of the external seminal grooves (Fig. 14.12). These sperm pathways are 

 protected by their positions during the temporary union and by mucous sheets 

 with which the two worms cover these regions of their bodies at the time of 

 mating. The female portions of the system do not function until later, when 

 eggs are emitted to the exterior and fertilization occurs. At such times a 

 girdle-like cocoon is secreted by the glandular cells of the clitellum and then 

 moved anteriorly by peristaltic contractions of the body. As this cocoon 

 passes segment 14, ova are deposited within it from the openings of the ovi- 

 ducts. As it passes the openings of the seminal receptacles, farther anteri- 

 orlv, spermatozoa received during copulation are likewise discharged into the 

 space between the girdle and the body wall, and fertilization occurs. Finally, 



Fig. 14.11. Dorsal view 

 of the reproductive system 

 of the earthworm; semi- 

 diaetrammatic. The cavities 

 of the seminal vesicles have 

 been expo.sed on the ris;ht 

 side, revealing the testes and 

 the funnels of the ductus 

 efferentes. 



Oviduct 



Nephridium 



Seminal 

 receptacle 



Ovisac 



Nerve cord 



411 



