i68 



GENERAL BIOLOGY 



arate only on the sides and above, being united across the 

 median Hne below the enteron. They contain the sper- 

 maries, and usually a large mass of sperm cells in the later 

 stages of development liberated therefrom. If one slit open 

 a vesicle and take from it a drop of its whitish fluid contents 

 and mount this in a drop of normal salt solution for the 

 micoscope he will see abundant sperm cells. They 

 deverlop in berry-Hke clusters of ovoid cells, which gradually 



lengthen out into a flagellum- 

 like tail at their distal ends, and 

 finally break apart and swim 

 free. They pass down the sperm 

 ducts to the external openings 

 already seen on the ventral side 

 of segment fifteen. Their first 

 destination is the sperm recep- 

 tacles of another worm. These 

 receptacles may be seen on the 

 floor of the body cavity at either 

 side of the foremost sperm 

 vesicle, two pairs of whitish or 

 yellowish sacs, whose outlets are 

 at front and hind margins of seg- 

 ment ten. 



The sperms are extruded in 

 copulation, when two worms 

 come together in reversed position, so that the A'entral sur- 

 faces of segments ten and fifteen are opposed to each other. 

 The sperm cells of each worm are passed out and into the 

 sperm receptacles of the other worm. This is preliminary 

 to fertilization. 



The eggs are produced in simple ovaries that lie in the 

 thirteenth segment, attached near the nerve cord to the 

 septum in front. When mature they break away and lie 



Fig. 105. Diagram of reproduc- 

 tive organs of the earth worm, 

 as viewed from above, the body 

 wall outspread, and the enteron 

 removed. a, nerve branches; 

 b, nerve cord; c, sperm 

 receptacles, d, d, d, sperm vesi- 

 cles; e, e, spermaries(two pairs) ; 

 /, sperm duct;g, g, ovaries;/:, h, 

 oviducts; i, nephridium. Serial 

 number of segments indicated 

 at left. 



