496 ERNEST W. L. HOLT, 



morphological significance as the dorsal vesicle (or parietal eye) in 

 Fetromyzon. There is certainly some resemblance between the two 

 structures, but I think that this is, so to speak, accidental, and that, 

 in the Herring, the constriction is to be regarded merely as an exagger- 

 ation of that folding of the pineal walls which occurs in other Tele- 

 osteans, as shown by E,ABL-RtJOKHAED in Salmo (7, Taf. VII, figs. 17 

 -19). 



I have shown (p. 492) that in the early post-larval Herring the 

 pineal body, as yet solid, receives fibres from the optic thalami 

 (fig. 11 t. 0.) by way of the superior commissure (c. s.) and also 

 (fig. 10 ß.) by way of the labium. In the 1^^ inch stage fibres 

 (fig. 19 fi.) still pass from the optic thalami to the hinder pineal wall 

 by way of the labium (t.f.), and this is equally the case in the post- 

 larval blenny (fig. 22 fi.). These facts derive some interest from the 

 following words of Beard on the parietal eye (4, p. 68): „I still hold 

 to the view that the organ has been developed in connection with the 

 paired eyes. For this conclusion the two sorts of end elements, rods 

 and cones, described by me in Fetromyzon^ are of importance; as is 

 also the fact that fibres have been traced from the optici thalami to 

 the epiphysis." 



My researches were undertaken with a view of ultimately working 

 at Clupeoid anatomy in the Normal School of Science and Royal School 

 of Mines, South Kensington, at the suggestion of my teacher, Professor 

 Howes. My best thanks are due to Professors Mc Intosh and Howes 

 for criticism and advice, to Professor Mc Intosh for the use of the 

 St. Andrew's Marine Laboratory and of the University library, while 

 to Professor Howes, and to his demonstrator, Mr. M. F. Woodward, 

 my acknowledgements are due for their kindness in procuring me 

 books and references. 



