460 



The Animal Kingdom 



tightly by these special setae and secretions. Another close connection is 

 made between segments 26 of one worm and 15 of the other. The 

 grooves between segment 15 and the clitellum form a passageway for 

 sperm which enters the seminal receptacle of the other worm. After 

 two or three hours the worms separate. 



PBOSTOMIUM 

 PtBISTOMIUM 



OPENNGS OF. 



SEMINAL 

 RECEPTACLES 

 OPENING OF. 

 OVIDUCT 





CLITELLUM. 



A 



Fig. 150. — The earthworm, Lumbricus terrestris. A, Ventral view of anterior 

 portion; B, diagram illustrating copulation; C, cocoon containing eggs; D, diagram 

 of cross section of two earthworms in copulation. 



Around somites 9 to 36 a slime tube is formed by each worm. Inside 

 this, around the clitellum, is formed a cocoon. The slime tube contain- 

 ing the cocoon gradually slips forward and the sperm are picked up from 

 the seminal receptacle. The worm withdraws and the lemon-shaped 

 cocoon closes at both ends. It is left in the moist earth. Fertilization 

 occurs within the cocoon, and development is direct with no intervening 

 larval stages. 



The Biology of L. terrestris. — Scattered over the body surface, 

 but concentrated to some extent at the anterior end, are many sense 

 receptors. By means of these, the earthworms react to chemicals, heat, 

 light, moisture, and pressure. They show a positive reaction to food and 

 a negative one to irritating chemicals. Earthworms demonstrate a nega- 



