ISO DISCOVERY REPORTS 



medulla oblongata are established, and on the roof and floor respectively of the thala- 

 mencephalon the pineal and pituitary bodies can be clearly discerned. The roots of 

 most of the cranial nerves may also be found by dissection (Fig. 4 a). 



Between stages 31 and 34, the hemispheres grow rapidly and encroach on the 

 region of the thalamencephalon. They develop in association with the olfactory sense 

 organs at the time when the beak itself is elongating most noticeably (Fig. 4 b). Mean- 

 while the cerebellum {ce) makes its appearance behind the optic lobes. At first it is little 

 more than a ridge, and it develops late, as might be expected of an organ particularly 

 connected with the control and perception of fine movements. 



Further increase in the size of the hemispheres and of the cerebellum results in the 

 disposition of the main regions of the brain as illustrated in Fig. 4 c. The cerebellum, 

 now prominent, is divided by three sulci, the hindmost of which demarcates a broad 

 basal segment bearing a pair of lateral processes known as the flocculi. These are par- 

 ticularly clear at this stage (cf. the dorsal view of the brain shown in Fig. 5 b), and they 



a b c 



Fig. 5. Dorsal surface of the brain, a, of a Gentoo penguin embryo, stage 25 ; 6, of a Ring penguin embryo, 

 stage 37; c, of a Ring penguin embryo on the point of hatching (Plate VI). Scale: a x 6,b x ^i, c ,< zh 



are protected in a special recess which develops on the inner wall of the auditory 

 capsule. The close association of processes of the cerebellum with the otocyst in develop- 

 ment may have some functional significance, in view of the future relations of both 

 organs to movement. It is also noteworthy that in Crocodilia, the only reptiles which 

 have the cerebellum at all well developed, two sulci may be distinguished ; and in them 

 again the basal segment of the cerebellum bears a pair of flocculi (Heilmann, 1926, p. 108). 

 At the time of hatching (Fig. 5 c) the cerebellum has grown to such an extent that it 

 forms with the hemispheres the main mass of the brain. The efl'ect of this growth is to 

 push aside the optic lobes permanently, and the surface of the cerebellum becomes 

 marked by numerous sulci. This surface sculpturing makes a strong contrast between 

 the cerebellum and the hemispheres. The latter remain perfectly smooth without any 

 trace of convolution, and wedged in between them and the cerebellum may be seen the 

 tip of the pineal body. 



