TUNIC ATA. 



235 



chamber^ called the atrial chamber [atrium = entrance 

 hall) J which may be continued far down into the stalk 

 of the animal. 



Not far from the mouth is another opening, called 

 the atrial pore, or exhalent pore (cloacal opening), 



Pig, S3.— Simple AECidian, one of the Sea-squirts (halt natural size) : a, in- 

 current aperture ; b, excurrent aperture. 



which expires the water that has served for respir- 

 ation, carrying also with it the excretory products 

 which are expelled into the atrial chamber by the 



rig, 8i.— Larval Ascidian, showing urochord, i.e., homologue of the verte- 

 brate notoohord. Doliotam larva, one of the Thaliacese, with larval tail; ch. 

 chorda (urochord). 



