NERVOUS SYSTEM. 



71 



epidermal nerve-plexus of that organ. This is specially de- 

 veloped round the stalk of the proboscis to form the somewhat 



FIG. 58. Transverse section through the collar nerve cord of Glossobalanus sarniensis. 

 showing the central canal c with its cuticular lining ; ga giant ganglion cell, dw dorsal rout. 



ill-defined structure which is frequently spoken of as the proboscis 

 nerve-ring. The part of the dorsal cord contained in the collar 

 has different relations from the rest of the nerve trunks. It 



nc 



FIG. 59. Transverse section of the collar nerve cord of Glossobalanus minutus (after Spengel). 

 showing two of the isolated cavities with their cuticular lining, and the radiating lines sur- 

 rounding them ; nc canals in the fibrous substances which contained processes of the giant 

 cells. 



lies in the ventral wall of a tube or rod (Figs. 58, 59, 60) of 

 ectoderm which is derived in the embryo from the delamination 



