FIG. 21. Horizontal section of 

 normal trout embryo (PI. I. fig. i). 

 The section passes through the upper 

 parts of the eyes, and the auditory 

 organs, as well as through the various 

 cavities of the brain, and the central 

 canal of the spinal cord. Compare 

 with PI. X. figs. 39, 40 (union at optic 

 lobes), XII. fig. 43 (union at medulla), 

 and with PI. XV. fig. 53 (union in 

 pectoral region). For other references 

 see under PI. I. fig. i. ( x 13. ) 



FIG. 22. Horizontal section as 

 above, but passing below the cavities 

 of the optic lobes and the medulla, 

 and cutting through the middle of the 

 eyes and the auditory organs. Com- 

 pare with PI XII. figs. 44, 45 (union 

 at medulla). Other references under 

 PI. I. fig. i. (xi 3 .) 



FIG. 23. Horizontal section as 

 above, but passing through the lower 

 parts of the eyes, brain, and auditory 

 organs, as well as through the head- 

 kidney, the duct of the swim-bladder, 

 and the dorsal portions of the gill 

 arches, and of the body cavity. Com- 

 pare with Pis. XI., XII. figs. 42, 45, 

 46 (union at optic lobes, and at 

 medulla). Other references under 

 PI. I. fig. i. (xi 3 .) 





PL. V. 



