EGG-LAYING. 145 



The seminal receptacles are accessory organs of reproduction 

 in the shape of small rounded sacs or pouches, open to the 

 outside only, at about the level of the upper row of setse. They 

 lie between the 9th and 10th, and 10th and llth somites (s.r, 

 ' Figs. 75 and 80), where their openings may be sought for 

 (Fig. 72). Their function is explained under the head of copula- 

 tion. 



Accessory glands. Besides all the structures so far described 

 there are many glands which play a part in the reproductive 

 functions. The setigerous glands from about the 7th to about 

 the 19th somite (sometimes fewer, sometimes none at all) are 

 often greatly enlarged, and form the glandular prominences men- 

 tioned at p. 121. They seem to be nsed as organs of adhesion 

 during copulation. The clitellum is filled with gland-cells which 

 probably serve in part to secrete a nourishing fluid for the young 

 worms, and in part to provide a tough protecting membrane to 

 cover them. 



Copulation. Egg-laying;. Inasmuch as each individual earth- 

 worm produces both ova and spermatozoa, it might be sup- 

 posed that copulation, or the sexual union of two different 

 individuals, would not be needful. This, however, is not the 

 case. The ova of one individual are invariably fertilized by 

 the spermatozoa of another individual after a process of copu- 

 lation and exchange of spermatozoa, as follows : During the 

 night-time, and usually in the spring, the worms leave their bur- 

 rows and pair, placing themselves so that their heads point in 

 opposite directions and holding firmly together by the enlarged 

 setigerous glands and the thickened lower lateral margins of 

 the clitellum. During this act the seminal receptacles of each 

 worm are filled with spermatozoa from the sperm-ducts of the 

 other, after which the worms separate. 



When the worm is ready to lay its eggs the glands of the cli- 

 tellum become very active, pouring out a thick glairy fluid which 

 soon hardens into a tough membrane and forms a girdle around 

 the body. Besides this a large quantity of a thick jelly-like nu- 

 trient fluid is poured out and retained in the space between the 

 girdle and the body of the worm. The girdle is thereupon grad- 

 ually worked forward toward the head of the worm by contrac- 

 tions of the body. As it passes the 14th somite a number of ova 

 are received from the oviducts, and between the 9th and llth 

 10 



