PARIETAL EYE AND ADJACENT ORGANS IN STHENODON. 143 



to notice one point very carefully. The commissure which 

 Ritter identifies as the superior commissure evidently does 

 not correspond with tliat structure as described by Hill in 

 fishes and myself in Sphenodon. It corresponds rather to 

 what I have identified as the commissura fornicis in 

 Sphenodon. Where, then, are we to look for the superior 

 commissure in Phrynosoraa? I believe that it has united 

 with the posterior commissure in the manner already indi- 

 cated. This interpretation renders Emitter's figure directly 

 comparable with mine. 



Further evidence in favour of my views on this subject is 

 afforded by my fig. 28, representing, in a slightly diagram- 

 matic manner, a sagittal section through the third ventricle 

 and neighbouring organs in Hinulia. 



(/) The Paraphysis. 



In the interpretation of the so-called " epiphysis " or '' pineal 

 gland" of the higher vertebrates, the paraphysis, only discovered 

 within recent years, must in future play a very important part. 

 An excellent summary of the history of our knowledge of this 

 organ has been given by Studnicka (37). From this it 

 appears that Selenka, whose original paper ^ I have been 

 unable to see, gave the name ^'paraphysis'' to an unpaired 

 outgrowth of the membranous roof of the prosencephalon in 

 embryos of reptiles and Selachians. He interpreted this 

 structure as a rudimentary sense-organ, and homologised it 

 with the auditory organ of Ascidians, as Spencer and de Graaf 

 had previously homologised the epiphysis with the eye. 



The organ itself had been found previously by Hoffmann 

 in Tropidonotus and Lacerta, and by Francotte ^ in 

 Anguis, the latter interpreting it as the choroid plexus. It 

 has since been found in representatives of almost all vertebrate 



1 " Das Slirnorgan der Wirbelthiere," 'Biol. Centralblatt,' x. 



2 " Weitere Uutersueliungen zur Entwicklung der Reptilien," ' Morpli. 

 Jahrb.,' xi. 



^ " Recherclies sur la Developpement d I'Epipliyse," ' Archiv. de Biologie,' 

 viii. 



VOL. 42, PART 2. NKW SERIES. K 



