io6 



VERTEBRATES WITHOUT JAWS 



carried in the large tract that proceeds from the habenular ganglion 

 to the hypothalamus, in the floor of the diencephalon. The latter is 

 known to be concerned, throughout the vertebrate series, with the 

 integration of the internal activities of the animal. 



¥ d Y 





pner. 



p. int. 



pant 



Fig. 68. Sagittal section of the pituitary gland of lamprey. 



dien. diencephalon; inf. infundibulum; p.ant., p.int., and p. tier, partes anterior, intermedia, 



and nervosa, there are two types of cell in the pars anterior; 3rd V. third ventricle. 



(After Stendell.) 



3 4 5 6 



Hours after operation 



FlG. 69. Onset of pallor in a larval lamprey after removal of the pituitary gland, 

 as shown by the decline in the melanophore index. (From Young.) 



1 1 . Pituitary body and hypophysial sac 



The lower portion of the diencephalon, the hypothalamus, forms 

 a prominent pair of sacs, the lobi inferiores, which contain a partly 

 separated diverticulum of the third ventricle and end below in the 

 infundibulum (Fig. 65). The pituitary gland (hypophysis) is pressed 

 against the underside of the hypothalamus (Fig. 68). The lower wall 

 of the brain in this region consists not of nerve-cells but of a single 



