STAGE "E". 00 HOURS. 



The thickening of the ventral ectoderm which 

 was begun in "D" has continued luring the si:: houhs 

 which intervene between "D" and "E" and has spread 

 tc the sides or the larva, Figs. 15. and 10-21. 



r the edge of this thickened oral disk arc- 

 to be found five groups of rounded elevations of 

 the ectoderm. The three elevations, of which each 

 group consists, form the angles of an isoceles tri- 

 angle .the apex of which points away from the mouth 

 of the larva. Fig. 15. These elevations^ or evagin- 

 ated papsllae^lie immediately below and enclose the 

 tips of those branches of the radial water canals 

 which form the rudiments of the end tentacle and 

 first pair of foot tentacles of each arm .Figs 10. 

 and 21. In this way each tentacle grows into its 

 ectoderm, the latter closing around it as it pushes 

 out. 



The function of these tentacles in the adult 

 being mainly a sensory one, it is interesting to 

 note that they receive their ectoderm from part of 

 the same thickened oral area v/hich gives rise later 

 to the adult nervous system. 



The ciliated bands in "E" do not differ in ap- 



