200 



GENERAL BIOLOGY 



Fig. 126. Older salamander larva, showing further development of the gills. 

 a, anus; b, gills; c, opercular fold; d, nostril; e, mouth; /. /, caudal fin; 



growth of the two lobes forward and extension of the ex- 

 panded canal into them, the hollow cerebral hemispheres are 

 formed; the small olfactory lobes grow forward from 

 beneath their anterior ends. At the rear of the hemispheres 

 on the middorsal line a small process grows upward to 

 become the pineal body — a vestigial structure, correspond- 

 ing to the nervous apparatus of a median eye, that is 

 functional in some lizards. A hollow downgrowth on the 

 midventral line develops the infundibulum. This connects 

 with the pituitary body, developed in the roof of the mouth. 

 Paired upgrowths from the lateral wall of the midbrain 

 become the optic lobes of the brain. The central cavity 

 extends into each of these, the expansions of it within the 

 optic lobes being known as optic ventricles. An axial dila- 



FiG. 127. Older larva of the spotted salamander, with legs developed. 



tation of the central canal (fig. 1 18 2;) is known as the third 

 ventricle. From the front end of the third of the primary 

 brain divisions the cerebellum arises as a transverse solid 

 upgrowing ridge of tissue upon the dorsal side. Just 

 behind this lies the fourth ventricle, as already noted (fig. 

 iiSw). It appears from above as a triangular dilatation 



