Ojptic Lobes of Foivl. 89 



dorsal surface, and is approximated to the cereln-al hemispheres, 

 which are still growing back posteriorly. Ten convolutions are 

 apparent in the lateral view. The ventro-la.teral depressions of 

 the cerebral hemispheres are becoming less marked. The 

 medulla is much as at the preceding stage. 



9c (Fig. 9, Section 1) is taken across the anterior portion of 

 the optic lobes in such a way as to show the optocoele, now 

 rendered crescent-shaped and much smaller by the great increase 

 in the brain substance. Above the optic lobes is seen the hinder 

 portion of the cerebral hemispheres, now growing over the optic 

 lobes from before back, and tending to hide them from view 

 dorsally. The epiphysis is visible in the mid-dorsal line of this 

 figure. 



9d (Fig. 9, Section 2) is a section across the centre of the 

 region of the optic lobes. It shows a marked increase in the 

 size of the cerebellum, together with the decidedly lateral posi- 

 tion now assumed by the optic lobes. 



9e (Fig. 9. Section 3) is a cut across the posterior part of the 

 region of the optic lobes. It shows the most posterior portion 

 of the optic lobes, the cavity of which is not seen, the section 

 being taken so far back as to cut through the brain substance 

 only. The cerebellum is very definite in the mid-dorsal line, 

 and has assumed almost adult proportions. 



Stage X. (PI. XXXIV.) 



The tenth stage corresponds approximately with a period of 

 20 days' incubation. 



In the dorsal aspect (10b) there will be seen a marked differ- 

 ence in the size of the brain. The cerebral hemispheres are 

 overshadowing the optic lobes very markedly from the anterior, 

 and the cerebellum is also growing over them from the middle 

 outwards. The optic lobes can now scarcely be called latero- 

 dorsal structures, but rather latero-ventral. In the cerebellum 

 nine well-developed convolutions are visible, and the flocculi 

 are well marked. The epiphysis, though still present, is now 

 but faintly seen, and is sunk in between the posterior portions 

 of the cerebral hemispheres and the anterior part of the cere- 

 bellum. 



