228 W. BALDWIN SPENCEE. 



Whilst it must be admitted that we are without evidence 

 sufficient to warrant us in regarding the pineal as the direct 

 representative of the azygos Tunicate eye, it is, perhaps, 

 worth suggesting that there may be some connection between 

 the larval eye ofTunicata and the epiphysis of higher 

 forms. It maybe pointed out, first of all, that the position 

 of the eye and that of the rudiment of the epiphysis is the 

 same with regard to the anterior end of the notochord, both, 

 further, being situated on the dorsal surface of the '' brain," 

 applying this term to the anterior vesicle of the neural canal 

 in Tunic at a. It must, however, be also noticed that the eye 

 of the latter is placed not exactly medianly, but slightly to the 

 right side.^ There still remains the great difficulty of the 

 transformation of the internally placed eye into an external 

 hollow process of the brain roof. 



According to Kowalewsky,^ the Tunicate eye first appears as 

 a thickening of the dorsal wall of the brain cavity, in 

 one particular portion the cells becoming cylin- 

 drical and much elongated, and pigment appearing at 

 their internal ends. The refractive structures forming the 

 lens are produced subsequently, so that at first the eye is 

 merely a specially thickened part of the roof of the brain 

 cavity, and only at a later period appears to assume its dis- 

 tinctly internal position, bulging out into the cavity (cf. figs. 

 32, 34). 



Turning now to the epiphysis, we find that it arises as a 

 hollow outgrowth from the brain roof, presenting, as a rule, 

 nothing comparable to the structure of the Tunicate eye. In 

 one form, however, amongst Amphibia, it is just possible 

 that we meet with an indication of a connection existing be- 

 tween the two. A further examination in other forms, par- 

 ticularly those of Pisces, might possibly reveal a similar 



1 Ahlbom draws attention to the slightly asymmetrical position of the 

 epiphysis in Petromyzon, where it becomes, by secondary growth, united to 

 the left ganglion habenulse ; but since the eye of Tunicates is on the right 

 side, it is difficult to imagine any connection between the two. 



» ' Arch. f. Mikr. Anat.,' Bd. vii, 1871, pi. xii, figs. 32 and 34. 



