142 



THE FLATWORMS— PLATYHELMINTHES 



structure and function to those of man. They are still hermaphroditic, 

 so we find a complete set of both male and female organs in each animal. 

 Fig. 10.6 shows these organs and their relationships to each other. Since 

 planaria is bilateral, each set of organs is duplicated on either side with 

 the exception of those in the center, but in the diagram only one sex is 

 shown on each side to avoid confusion that would exist if the organs 



Ovary 



Oviduct 



Yolk gland 



Seminal 

 receptacle 



Vagina 



Testes 



Vasa efferentia 



Vas deferens 



Seminal vesicle 



Penis 



Genital atrium 



Genital pore 



Fig. 10.6. The reproductive system of planaria. Male organs are shown on the right 

 and female organs on the left to prevent confusion of the two. Both sets of organs are 



the same on either side. 



were shown overlapping one another. All the organs necessary for 

 sexual reproduction are present in each animal, yet there is sexual union 

 between two animals in which sperms are exchanged. This act is called 

 copulation, which is a term used to describe the union between two ani- 

 mals in which sperms are transferred from one to the other and applies 

 to all forms of animal life. 



