The Comparative Physiology of the Pituitary Body 269 



latter being comparative!}^ small in amount. In the anterior part of the 

 pituitary a somewhat quadrilateral or wedge-shaped mass is characterised 

 by the large and deeply staining cells of which it is composed. These cells 

 are almost identical in appearance with the cells found in the anterior lobe 

 of the mammalian pituitary, and the portion containing them is probably 

 the equivalent of the true anterior lobe. The cells are arranged in columns 

 with blood-channels between. There is no trace of tubules, and nothing 

 to support Haller's contention that the anterior lobe of the teleostean 

 pituitary is a tubular gland secreting into the subdural space. This portion 

 of the pituitary of the cod corresponds with that described by Sterzi in 

 other bony fishes as the chromophil segment. Gentes also noted the deeply 

 staining cells met with in certain positions in the teleostean pituitary, and 

 showed that they vary in situation and extent in different species. The 

 chromophil portion is aggregated in the cod's pituitary in the position 

 indicated in fig. 2, c, of Plate. It may be regarded as constituting the true 

 anterior lobe, and its similarity to the anterior lobe of the mammalian 

 pituitary suggests that it has a like function. 



The other epithelial constituent of the cod's pituitary is widely dis- 

 tributed in the form of small round cells which have little affinity for 

 stains. They surround and invade the nervous tissue of the pituitary, and 

 resemble in this respect the cells of the pars intermedia of the mammalian 

 organ. This part of the gland was described by Sterzi as the "chromo- 

 phobe " portion, and there is little doubt that it corresponds with the pars 

 intermedia of mammals and birds. Gentes found it in the types he 

 examined, and states that it surrounds and passes between projections of 

 the nervous substance of the infundibular lobe. The pars intermedia in 

 the cod is divided into two main portions, which are continuous with, and 

 separated from one another by, the true anterior lobe. The part which 

 lies in front of the chromophil segment consists of a mass of small cells 

 among which fibres of the nervous substance penetrate. The latter 

 increases in amount towards the junction of the pituitary with the brain 

 substance behind the optic nerves. The thin lamina of nervous tissue 

 connecting the pituitary with the brain in this situation is called by 

 Gentes the lamina post-optica. The main mass of the pars intermedia lies 

 behind the chromophil portion and makes up the greater part of the lobe. 

 On the surface of the pituitary the epithelial cells form a thick mass and 

 pass deeply inwards among the fibres of the nervous portion. 



The pars nervosa of the cod's pituitary is small in amount, and appears 

 to be composed of neuroglia and ependyma cells, without any true nerve 

 cells. It is continuous with the brain in front by the lamina post-optica 

 or anterior lamina, and at the sides by lateral laTninae. A thin layer of 

 nervous tissue separates the chromophil substance from the cavity of the 

 infundibulum. Behind and in the middle line the pituitary is continued 

 into the wall of the saccus vasculosus. The nervous substance of the 

 pituitary closely resembles in structure the pars nervosa of the mammalian 



