SAEGENT: the optic KEFLEX APPARATUS OF VERTEBRATES. 189 



the axons and fibrils formed from the coalesced axons of the optic reflex 

 cells emerge, and joining within it form Reissner's fibre (Plate 6, Fig. 

 40, rec. ms^coel.). 



^^cras.e'end. 



Figure C. Amia calva, larva of thirty days. Diagrammatic sagittal section of the 

 anterior portion of the midbrain roof. X 87. For meaning of abbreviations, 

 see Explanation of Plates, p. 257. 



The cells in the adult have an average diameter of 18 micra, about 

 the same as in the larval stages, and are consequently much smaller than 

 in Polypterus. In addition to the axon, there are two principal neurites 



Figured. Amia calva, adult. Diagrammatic sagittal section of the same region 

 as in Figure C. X 41. A comparison of the two figures illustrates the 

 morphological changes affecting the position of the tectal reflex cells and the 

 surrounding brain structures in the transition from larval to adult conditions. 

 For meaning of abbreviations, see Explanation of Plates, p. 257. 



given off from the cells and a number of finer dendrites. These two 

 neurites can sometimes be traced for a considerable distance. They pro- 

 ceed dorsad and laterad through the middle of the vertical portion of the 



