462 SCIENCE PROGRESS 



become differentiated in situ, the chromophilic cells appearing 

 first in the posterior region of the pars distalis (Parker, 16). 

 The origin of the pars tuberalis has already been briefly de- 

 scribed above. 



It is only possible to refer very briefly to the physiological 

 significance of the pituitary body (see Swale Vincent, 24). Oliver 

 and Schafer (15) found that saline extracts of the pituitary body, 

 when injected into the blood-stream, produce a rise in blood- 

 pressure. Pituitary extract has also been found to act speci- 

 fically on the kidneys, producing dilatation of the renal vessels 

 and increase of secretion from the tubules. From the results 

 of Herring (8), Howell (9), and others, it seems probable that 

 this effect is produced by the secretion of the posterior lobe, 

 and that the active principles of that lobe are products of the 

 epithelial cells of the pars infundibularis. Herring (8) finds 

 that the extract of the " anterior lobe " (pars distalis) in some 

 forms stimulates mammary glands to activity, but has no effect 

 on blood-pressure, kidney-volume, or urinary secretion. 



There seems to be good evidence for associating a patho- 

 logical condition of the pituitary with acromegaly, a disease 

 characterised by enlargement of the bones, especially of the 

 hands and feet, so that it seems possible that the pituitary is 

 an internally secreting gland, exercising some control over 

 growth of bone. 



Many problems relating to the origin and evolution of the 

 pituitary body have been left untouched in the foregoing, and 

 it is impossible to deal with them here. Embryological evi- 

 dence shows that the pars buccalis is derived from an ecto- 

 dermal invagination, and numerous hypotheses have been 

 advanced as to the original significance of this structure. 

 Amongst other theories it has been suggested that the hypo- 

 physis represents the mouth of the ancestor of the Vertebrates, 

 the costal gland of an Arthropod ancestor, the remains of 

 the proboscis of a Nemertean ancestor, a functional anterior 

 neuropore, a pair of gill-clefts, and so on. Nusbaum(i4) 

 described a connection between the hypophysis and the preoral 

 gut in dog embryos and put forward the theory that the two 

 structures represent remains of a portion of gut extending in 

 front of the present mouth in the ancestor of the Vertebrates. 

 In some Marsupials also the preoral gut is closely associated 

 with the hypophysis, but it is impossible at present to say 



