The epithelium at this point is pigmented and forms the first 

 rudiment of the eye, oc. Fig. loa. Fig. IG illustrates a 

 more advanced stage where the proximal part of the tentacle is 

 beginning to take on its final shape and is separated by a pro- 

 nounced band from the distal pai't, which is still functional 

 as a tentacle. 



We come finally to a stage in which, while the long dis- 

 tal part of the tentacle retains its characteristic structure 

 and remains completely functional, the short proximal part has 

 become completely differentiated into a rhopalium. Fig. 40 

 is from a longitudinal section of such a tentacle. The rho- 

 palial part has assumed nearly its final shape. The differ- 

 entiation of its ectoderm into sensory epithelium, eye spot, 

 and layer of nerve fibres, is canplete. It has a lumen that 

 extends outward to the solid chorda-like entoderm of the distal 

 part of the tentacle and opens towards tht centre into a gas- 

 tric pocket. The entoaej-mal lining of the lujuen is a colum- 

 nar epithelium, the more distal cells being deeper and contain- 

 ing the concretions. Compare Fig. 40 with Fig?.3S ana 39 which, 

 being interradial, are certainly destined to be rhopalial ten- 

 tacles. 



The growth of the marginal lobes, that when last mention- 

 ed were semicircular, has continued, and each lobe has now pro- 



- 42 - 



