ALIMENTARY SYSTEM *BODY CAVITY. 



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ALIMENTARY SYSTEM. SUMMARY 



Body cavity. In Amphioxus the ccelom arises as pouches 

 from the archenteron (enter occelic). In the other Vertebrates, 

 owing to modified processes of development, probably first 

 arising from the presence of much yolk, solid cell masses 

 grow out in place of hollow sacs, but the cavities which 

 appear later, apparently by splitting of the cell mass 

 (schizoccelic), are in reality the retarded cavities of true 

 ccelom-pouches. A dorsal segmented portion (protoverte- 

 brae) becomes separated off from a ventral unsegmented 

 portion (Fig. 255). It is this ventral portion which forms 

 the body cavity of the adult. In the adult it is divided 

 into an anterior pericardial and a posterior peritoneal 

 portion. 



The body cavity may form part of one or all of the following systems : 

 (l) excretory, voiding waste by abdominal pores or by nephrostomes ; 

 (2) reproductive, receiving the liberated genital elements ; and (3) 

 lymphatic, receiving translations from visceral and abdominal organs. 



