Proboscis 



Pericardium' 

 Heart 



Glomerulus — i 



■*- -< Collar ■ 



Dorsal pore 



-Trunk *- 



Dorsal nerve cord 



I — Dorsal blood vessel 

 Respiratory pharynx 



1 Gonad 



Proboscis coelom 



'Notochord" 



Mouth 



Gill slit-" 



'-Nutritive pha 

 Ventral blood vessel 

 Ventral nerve cord 



Figure 204. Acorn worm [Glossobalanus] . A, longitudinal section through the middle line. 

 Some zoologists call the short anterior structure, which has long been called a notochord, a 

 "stomochord," but this new name does not rule out the possibility of its being homologous with 

 the notochord of the vertebrates. B, cross section through the trunk region. (A modified from 

 Bullock; B after Bullock.) 



IncorrenT siphon 



Tunic 



Mantle 

 Pharyngeal slit 



Endostyle with 

 cilia 



Pharyngeal 

 sac 



Excurrent siphon 



Nerve ganglion 

 Gland 



Atrial cavity 

 Anus 



Rectum 

 Duct of gonad 



T^ Esophagus 



I Ovary 



— Testis 



Digestive gland 



Figure 205. Internal structure of a tunicate {Molgula). Tunic, mantle, and pharynx removed 

 from left side. Arrows indicate flow of water currents through the animal. 



322 



