34 



FREDERICK TILNEY AND LUTHER F. WARREN 



detached distal portion of the epiphysis, the homologue of the 

 frontal gland in amphibians. The idea advanced by Strahl was 

 subsequently confirmed by Hoffmann 186 in 1886 and again by 

 Beraneck 21 in 1887. But it is to deGraaf 155 that we are indebted 

 for the first demonstration that the organ of Leydig was pro- 

 vided with a lens and a retina and was, hence, a real visual organ. 

 This work of deGraaf in 1886 was almost simultaneously con- 



Fig. 5 Scheraatization of the pineal region in Sphenodon, according to Stud- 

 nicka, 1905. 



Ls., lamina terminalis; V., velum transversum; Pf., paraphysis; Ds., dorsal 

 sac; Ch., co.nmissura habenularis ; I'd., parapineal organ; Npar., nervus parapi- 

 nealis; !'<>., pineal organ; Ep., proximal portion pineal organ; T 'p., tractus pinealis; 

 Sch., pars intercalaris posterior; Cp., comrnissura posterior; M., inidbrain, A'/*., 

 accessory parapineal organ; l\., Krrrssus pinralis. 



firmed in the same year by Spencer 366 who carried on a large 

 number of observations upon many different Saurian forms, 

 confirming in detail the proposition advanced by deGraaf that 

 the structure described by Leydig as the frontal organ contained 

 nol only a lens, but a definite retina. These works led up to 

 the later investigations on the parietal eye and also on what has 

 been called the third eye of vertebrates. 



