EARTHWORM 



358 



vesicals and vas deferens to the dosed passage and move through it 

 to the seminal receptacles of the mate, where they are stored. In 

 the meantime, the clitellum of each individual secretes a band which 

 binds them together at these two points. After each has received 

 sperms from the other, they separate by working themselves through 

 the bands secreted by the clitella. This leaves each animal with a 

 band which is gradually worked off toward the anterior end. As 

 the band passes over the openings of the oviducts, eggs are released 

 into it, and as it passes the openings of the seminal receptacles, 

 sperms, which came from the reproductive mate, are released. 



fipertures of flpertare of • 



Seminal receptacles Vas deferens CliteUam 



Seminal droove Pore of ovidact 



Dorsal 

 blood vessel 



Body wall 



Intestine 



3en?ina/ 

 groove 



Band of 

 macus 

 secreted by 

 a clitellum 



Fig. 130. — Reproduction in earthworm showing copulation and cocoon. A, Two 

 worms enclosed in bands of mucus during copulation ; B, transverse section show- 

 ing the seminal grooves ; C, cocoon. 



Both ends of the band close, forming a cocoon in which fertiliza- 

 tion and development take place. 



Cleavage in earthworms is of the unequal holoblastic type. Soon 

 after the segmentation cavity is formed, a certain cell, known as the 

 mesohlast cell, is set off, and the cells resulting from its divisions 

 move into the cleavage cavity, and will form the mesoderm. As the 

 mesoblast cells move into the cleavage cavity, gastrulation occurs 

 by invagination to form the endoderm and ectoderm. The gastrula 

 elongates and the archenteron opens at both ends to form the mouth 



