256 



THE RISE OF ANIMAL LIFE 



nznal pore 



qcniial ponz 



ODfarioroddudor. 



ankriorqQiTqIion 



mcxitb 



bbial palps 



pedal 



qanqlioo 



itTtcstirw 



stonoacb 



pericQrdialcaN)iiyik'd"^stcriorQortQ 



posterior retractor 

 posterior adductor 

 onus 



posterior qanqlioD 

 vtotzr 



pcurrerT^ siphon 



rcntsipbof? 

 vyxrhzr 



shell 



side vievs) 



cutdqe of shell 



intestine 

 anterior aorta 



auricle 



openinq to kidney 



cut edge of mantle 

 anus 



excur rent siphon 



v^er 



cutcdqeofwjiTtlc. 



pericardial 

 CQViiy 



dorsal vicW 



iDcurnzTTl-siphoD 

 posrerior adductor 



posterior retractor 

 'cui-cdqeofqill 



Fig. 12-6. The internal anatomy of the clam shown from the side and dorsal views. 



arificially by inserting glass beads into the 

 mantles of clams or oysters. After several 

 years the pearls can be removed and sold 

 on the market. These are true pearls arti- 

 ficially produced (Fig. 12-5). 



Once the valves of the clam are opened, a 

 soft body enveloped in a mantle is exposed. 

 The mantle simply consists of two thin 



sheets of tissue, or lobes. The posterior free 

 ends are muscular, and come together to 

 form the ventral incurrent and the dorsal 

 excurrent siphons, which permit water to 

 move in and out by ciliary action of the 

 inner mantle cavity (Fig. 12-6). Each side 

 of the mantle adheres to the inner nacreous 

 surface of the two valves. At these points of 



