PRAEORAL LOBE. 



275 



came established between the nervous and digestive 

 systems, known respectively as the anterior and posterior 

 neurenteric canals. 



The posterior neurenteric canal is only of transitory 

 occurrence in all existing Vertebrates, and leads from the 







Fig. 131. Diagrammatic representations of the anterior region of the body 

 in (A) an Ascidian larva, (B) larva of Amphioxus, and (C) Balanoglossus. 

 (After WiLLEY.) 



The figure of Balanoglossus was compiled from Bateson's figures; the pro- 

 boscis-pore is indicated rather too far forwards. 



p.l. Praeoral lobe (fixing organ, snout, proboscis), end. Endostyle. p.p. Praeoral 

 pit or proboscis-pore, m. Mouth, np. Neuropore. nc. Medullary tube. ch. Noto- 

 chord. e. Eye. of. Otocyst. gl. and h. Proboscis-gland and proboscis-heart of 

 Balanoglossus 



