ON THE DEVELOPMENT OF LINGULA 'ANATINA. 



95 



Erker. 



anterior 



dorsal liver- 



otocy.-t,. 

 gastroparietal» 

 band 



posterior 

 dorsal liver 



seta 



shell 



exceedingly elongated ac- 

 companying the elonga- 

 tion of the alimentary 

 canal. 



7). The axis cells 

 of the nephridium have 

 increased in thickness 

 and are filled up with 

 secretion granules ; the 

 funnel has increased in 

 size and been separated 

 partly from the ileo- 

 parietal band. 



8). The otocyst has 

 become enclosed in the 

 thick layer of supporting 

 substance. 



9). In the peduncle 

 the muscle layer has 

 become extremely thick 

 while the epithelial layers 

 have thinned out. 



10). Both extremi- 

 ties of the arm-apparatus 

 have begun to coil owing 

 to the rapid growth of 

 those portions ; the cirri 

 have increased in size 

 and in number. The small arm-sinus has made its way to the 

 body cavity by means of a pair of fine canals, while the great 



..palliai sinns 



..epistorae 



-month 



..small arm-sinus 



-great arm-sinus 



■•subcesophagpal 



ganglion 

 -œsophagus 



-ventral liver 



•stomach 



-nephridium 



—.mid-gut 



— ileo-parietal band 

 —intestine 



..peduncle 



Diagram of median sagittal section through young 



Lingula (9 mm.). Organs not median 



are represented. X 12'5. 



