G36 Prof. Dendy. Structure, etc., of the Pineal Organs [June 22, 



wall of the dorsal sac and the anterior wall of the pineal sac, not far from 

 the lower extremity of the latter. Up to this point it consists of a well- 

 defined bundle of non-medullated nerve-fibres, with a definite sheath of 

 connective tissue in its more anterior portion, and with numerous elongated 

 nuclei lying between the nerve-fibres. It exactly resembles an ordinary 

 non-medullated nerve, and I can see no reason for regarding it as exhibiting 

 degeneration. The separate strands into which it breaks up at the point 

 mentioned, however, do- not contain the characteristic elongated nuclei, 

 which doubtless really belong to associated connective-tissue or nutrient 

 cells, and owing to the slenderness of these strands, and the difficulty of 

 distinguishing them from the connecti.ve-tissue fibres of the pia 'mater, I 

 have not succeeded in following them continuously to the brain in the adult 

 animal. 



In several series of sections of embryos of different ages, however, the 

 nerve has been traced to the brain as one continuous bundle of fibres 

 without difficulty, and it is quite clear that it enters the left liabenular 

 ganglion. It becomes closely attached to the roof of the dorsal sac, however, 

 before it reaches the habenular ganglion — or the spot where this will be 

 developed — and this fact probably explains why the lower part of the nerve 

 is broken up into separate strands in the adult, for the rapid growth of the 

 thin wall of the dorsal sac may be supposed to cause the spreading out of 

 the nerve-fibres over its surface. 



Nerve-fibres first appear in the retina of the pineal eye while the latter is 

 still resting upon the brain-roof, and I have come to the conclusion that they 

 grow from the retina to the brain as in the case of the lateral eye. 



A curious feature of the nerve of the pineal eye in tlie adult animal is 

 that it receives bundles of nerve-fibres from the wall of the pineal sac as 

 well as from the eye itself. This point has already been noted by Gisi. 



The left hal)enular ganglion in the adult is produced upwards to meet 

 the wall of the dorsal sac in a characteristic manner at a point where it 

 receives nerve-fibres from tlie latter in special al)undance. The right 

 habenular ganglion also receives fibres from the wall of the dorsal sac, 

 but is not produced upwards to the same extent as the left one. This 

 asymmetrical development of the habenular' ganglia further supports the 

 conclusion that tlie Mt habenular ganghon is especially associated with the 

 l)ineal eye. 



It is extremely difficult to form any conclusion as to how far the pineal 

 eye of Sphenodon still functions as a light-percipient organ. Such experi- 

 ments as liave hitherto been made have yielded entirely negative results. 

 The concentration of a I)right li^ht upon ihv. skin above the pineal eye 



