276 Herring 



prominent bilobed organ with a deep red colour due to the amount of blood 

 contained in its vessels. Its wall is thin and convoluted, and consists of 

 one or more layers of epithelial cells outside which are numerous and large 

 thin-walled blood-vessels. The epithelium is continued forwards into the 

 infundibulum, and in median sagittal section the common opening of the 

 two sacs is seen lying above and in front of the body of the pituitary. 

 The pituitary body of the skate is, then, an example of a type which is 

 entirely different from those of mammals, birds, and bony fishes. There is 

 no differentiation into anterior and posterior lobes, and the characteristics 

 of the cell elements of these are missing. The pituitary body itself fur- 

 nishes, as Gentes says, a schematic type of gland secreting into blood- 

 vessels. The posterior lobe is not distinct, but is represented to some 

 extent ; its infundibular surface appears to be largely devoted to the same 

 purposes as the saccus vasculosus. There are no colloid bodies present in 

 the thin layer of nervous substance, and no cells clearly resembling those 

 of the pars intermedia. 



Physiological Action of Extracts of the Pituitary and 

 OF THE Saccus Vasculosus of the Skate. 



The Pituitary Body. 



Extracts of the whole pituitary body of the skate have little effect upon 

 blood-pressure, kidney volume, or secretion of urine. Strong extracts pro- 

 duce a temporary fall of blood-pressure, but not a marked one (fig. 7). 

 Kidney volume is slightly increased, but there is no continuous expansion, 

 and the effect is merely that of the injection of Ringer's fluid. 



Kidney secretion is unaltered or very slightly increased. It is doubtful 

 if this increase is a specific one : it may be solely caused by the rapid 

 injection of so much fluid. The pituitary body of the skate apparently 

 contains none of the active principles which are found in the pars nervosa 

 and pars intermedia of mammals, birds, and teleosts. If any of these are 

 present, it is only in very small amount ; there is no clear evidence of a 

 histological character for the presence of these active principles, and it is 

 probable that they do not exist in the elasmobranch pituitary. 



The Saccus Vasculosus. 



Extracts of the saccus vasculosus, even when very concentrated, have 

 little effect. There may be, as in fig. 8, a temporary fall of blood-pressure, 

 but with weaker solutions there is no change. 



Kidney volume and urinary secretion may show a slight temporar}^ 

 increase, but, as was the case with extracts of the saccus vasculosus of the 

 cod, it is not a specific effect, but merely the result of the rapid injection 

 of so much Ringer's fluid. 



Extracts of portions of the brain adjacent to the pituitary body and 



