Art. XV. — The Pineal Eye of Mordacia mordax. 



With Woodcut. 



By Professoe W. Baldwin Spencer, M.A. 



[Read June 13, 1889.] 



In 1 883,* Ahlborn published an account of the structure of 

 the Pineal gland in the lamprey Petromyzon ; the discovery 

 and investigation of the structure of the Pineal eye in 

 Lacertilia some three years later, led Beardf to investigate- 

 the nature of the Pineal gland in Cyclostomata, and his full 

 results published in 1888 showed that, as in lizards, the 

 distal part of the gland was, in certain Cyclostomata, trans- 

 formed into an eye-like structure, though one not so highly 

 developed as in the former group. 



His work was done upon Petromyzon and the larval form 

 Ammocoetes, and upon Myxine. In these three lie founds 

 though not constantly, that pigment was deposited around 

 the cells forming the vesicle of the epiphysis. 



He was unable to secure a s])ecimen of the Australian 

 form Mordacia, and I am indebted to the kindness of 

 Professor McCoy for placing at my disposal a specimen of 

 the latter genus, upon an investigation of which this note 

 is liased. Tlie specimen was obtained in Victoria, and 

 Professor McCoy tells me that he has identified this with 

 the Tasmanian form. 



Ahlljorn had already described in detail the relationship 

 of the epiphysis to the brain and its union with the left 

 ganglion habenul^, and the division of its distal or vesicular 

 portion into two parts— an upper larger, and a lower smaller 

 vesicle. It was, in fact, simply Ahlborn's misfortune in not 

 meeting with a specimen in which dark pigment was 

 developed which prevented him from first discovering, by 



* " Untersuchuugen iiber das Gehirn von Petromyzonten." — Zcitschr. filr 

 Wiys. Zool, Bd. xxxix.. Heft. 2, 1883. 



t "The Parietal Eye of the Cyclostome Fishes:'— Q.J.M.S., 1888; alsa 

 Nature, July 14, 1887^ 



