PARIETAL EYE AND ADJACENT ORGANS IN SPHEXODON. 127 



the parapliysis. I have not been able to trace it to a coiiuec- 

 tion with the brain, but it certainly does not appear to be 

 connected with the apex of the parietal stalk. It is probably 

 not connected with the parietal stalk at all, though it lies 

 close under the antero-ventral surface of the latter. It 

 appears to contain elongated nuclei, but I am not quite certain 

 that these may not belong to surrounding connective-tissue 

 cells. 



I suspect that the nerve of the parietal eye grows downwards 

 and backwards from the outer layer of the retina^ and ulti- 

 mately becomes connected with the roof of the thalaraen- 

 cephalon. If this should prove to be the case we shall have 

 here another noteworthy resemblance between the parietal 

 eye and the ordinary paired eyes. 



The Paraphysis. — The relation of the parapliysis to the 

 other parts of the brain towards the end of Stage R is best 

 shown in fig. 15. It will be seen that the paraphysis arises 

 from the roof of the brain just in front of the commissura 

 fornicis. It curves upwards and backwards over the now 

 strongly arched and more or less folded roof of the third 

 ventricle. Its walls, which consist of short columnar cells 

 arranged in a single layer, are greatly folded and produced 

 into numerous blind diverticula^ which form a mass of some- 

 what convoluted tubules lying in front of the parietal stalk 

 and beneath the parietal eye. Intermingled with these tubules 

 are numerous blood-vessels, easily recognisable by the cor- 

 puscles which they contain, and the whole is bound together 

 by loose connective tissue. Histological details are shown in 

 fig. 16. It is worthy of note that the blood-corpuscles in this 

 region contain numerous small black pigment granules similar 

 to those which occur in the retina of the parietal eye and in 

 the parietal stalk. These pigment granules occur also in a 

 blood-vessel lying above the end of the parietal stalk, as shown 

 in fig. 16 (compare Bernard [7]). 



The paraphysis at this stage may also be advantageously 

 studied in transverse sections. Thus fig. 23 shows that it 

 originates from the same point as the choroid plexuses of the 



VOL. 42, PART 2. — NEW SERIES. I 



