THE PINEAL SYSTEM OF THE CHELONIA 287 



and there by connective tissue bundles derived from the capsule. The 

 lumen was lined by a single layer of cylindrical ependymal cells, which 

 were everywhere of the same size and ended at the same level on the inner 

 surface of the wall. The wall was composed of elongated ependymal 

 cells which were attached by their outer ends to the external limiting 

 membrane. The ependymal fibres tended to unite in bundles, which 

 gained attachment to the ingrowing fibres from the connective tissue 

 capsule. The tissue consists of peculiar stellate cells which send out 

 slender protoplasmic processes and probably correspond to neuroglia 

 cells, although no true neuroglial fibres are present. The cells are widely 

 separated from each other and the tissue thus has a somewhat spongy 

 appearance. There are no true ganglion cells, nor are any nerve-fibres 

 present. In many places the inner surface of the wall shows pits which 

 are due to small diverticula of the single central lumen ; external to 

 these are small closed cavities lying in the substance of the wall. Some- 

 times the diverticula and cavities are lined by cylindrical ependymal 

 cells, similar to those bounding the main cavity ; at others by the ordinary 

 cells of the surrounding tissue. There were no indications of a secretory 

 process in the walls of the epiphysis. In the central cavity some isolated 

 cells were found, the protoplasm of which seems to have been slightly 

 changed, and in the diverticula and spaces a few separate cells or small 

 amoeba-like syncytia were present. The stalk of the epiphysis had no 

 lumen, but small cavities similar to those in the body of the epiphysis 

 were present, and also spaces lying between the stellate cells which form 

 the bulk of the tissue of the stalk. No nervous cord could be seen in the 

 interior of the stalk. The epiphysis of the Chelonia thus appears to 

 occupy an intermediate position between that of the saurian reptiles and 

 that of birds. 



The pineal system of Crocodilia has already been alluded to (p. 47), 

 and it will only be necessary to note that the absence of the parietal 

 organ in all species examined is contrary to expectation in these animals 

 which live in tropical climates, should the theory of the function of the 

 parietal eye being an organ for the estimation of heat be correct. 



