PARIETAL EYE AND ADJACENT ORGANS IN SPHENODON. 131 



(4), Spencer (34), Studnicka (36), and others, upon the 

 structure and development of this organ in Cyclostoraes, as 

 well as those of the numerous observers who have studied it 

 in Lacertilia, afford conclusive evidence against Gaskell's 

 views; and the weight of this is now only increased by ray 

 own observations on Sphenodon, in which animal the 

 parietal eye certainly exhibits no trace of an Arthropod 

 character. 



(b) The Nerve of the Parietal Eye. 



The real nerve of the parietal eye appears, so far as I can 

 learn, to have been first discovered by Beraneck. I regret that 

 I have been unable to consult his earlier work on the subject,^ 

 but fortunately he has given an excellent account of his ob- 

 servations, together with a discussion of the question, in a 

 later paper (5), which I have been able to obtain. From this 

 I learn that Francotte, Strahl, and Martin have also observed 

 this nerve in Lacertilia. It appears, according to Beraneck, 

 that in An gu is fragilis the nerve is connected distally with 

 the retina of the parietal eye, and proximally with the roof of 

 the brain at a point which corresponds very closely with the 

 superior commissure as described by Hill (17) in fishes, by 

 Burckhardt (9) in Lacerta, and by myself in Sphenodon, 

 but which Beraneck terms the ''centre ou noyau parietal." 

 De Klinckowstrom (19) has also described the nerve of the 

 parietal eye in Iguana, and states that the '^ parietal centre" 

 from which it originates is situated asymmetrically on the 

 right side of the origin of the " epiphysis'^ (= parietal stalk). 

 In this connection it is worthy of note that Gaskell (12) 

 describes the nerve of the parietal eye in Ammocoetes as being 

 connected proximally with the right ganglion habenulse. 



Baldwin Spencer (33), as is well known, believed the nerve 

 of the parietal eye in Sphenodon to be formed from the 

 distal end of the '' epiphysis" (parietal stalk). This con- 

 clusion, strongly supported by Hoffmann (18), has, I under- 

 stand, been already challenged by Leydig, and my own 



1 " Ueber das Parietalauge der Reptilien," ' Jenaiscbe Zeitschrift,' 1887. 



