





F'lGS. 107 and 108. Sections through head of a cyclopio trout embryo, the former through the middle of the median eye 

 and its lens, and the latter through the entrance of the single optic nerve. This nerve is seen to divide at once into two 

 branches for the two partly separate retinae. The fused condition of the cerebral lobes will be noted, particularly in Fig. 107. 

 For details of structure see pp. 40-42. Compare also with the two succeeding figures, and with PI. XXVI. fig. in. (xa-j. ) 



FIGS. 109 and no. Transverse sections of the head of a trout embryo showing the condition of semi-cyclopia. There are 

 two eyes, but they are close together, and the optic nerve is single, although there are two choroidal fissures. The internal 

 recti are absent. As in typical cyclopia, the eyes intervene between the base of the brain and the trabeculae cranii, the 

 anterior ends of which are separated by a wide gap from the rudimentary olfactory capsular cartilages. The latter are not 

 shown in this section. Compare with the two preceding figures, and with PL XXVI. fig. in. See also p. 44. ( X24.) 



PL. XXV. 



