298 LIFE : OUTLINES OF GENERAL BIOLOGY 



the floor of the 'tween -brain — that small but important second 

 region of the brain, from which grow out the eyes and the pineal 

 body. But in the second place there is in development an earlier 

 hint of the pituitary body, namely, a pre-oral ingrowth of the 

 outer layer or ectoderm of the embryo. This ingrowth is solid in 

 lampreys, Hony Irishes, and amphibians; it is hollow in gristly fishes, 

 and in reptiles, birds, and mammals. It may arise within the 

 depression that forms the front of the mouth, but it has no real 

 connection with either mouth or nose. There are strong reasons for 

 regarding this ingrowth — the hypophysis, as it is technically called — 

 as represented by a ciliated pre-oral pit in the lancelet or Amphioxus. 

 If so, it is clearly one of the most ancient structures in our body. 



Whatever be its historical origin there is no doubt as to the 

 individual development of this part of the pituitary body; it is 

 an insinking of the superficial embryonic layer or ectoderm. Two 

 things happen. First, it comes into connection with the little down- 

 growth (the "infundibulum") from the 'tween-brain ; and second, 

 there is an acquisition of the endocrine mode of internal secretion. 

 The result is an intricate organ, partly nervous, partly glandular, 

 partly vascular — the pituitary body. In his monograph {Ihe Ana- 

 tomy, Histology, and Development of the Pituitary Body, OHver & 

 Boyd, 1926), Mr. de Beer gives an eloquent genealogical tree showing 

 the evolution of the organ through the Vertebrate series. It is 

 hardly a story that he who runs can read; but it rewards one to 

 spend some time in its scrutiny, for it shows very vividly how a 

 couple of small growths, neither very promisng to start with, 

 unite to form an organ that evolves into one of the main regulators 

 of our life. 



Experiments have confirmed a conclusion reached from the study 

 of disease, that the anterior part of the pituitary body, which is 

 of oral origin, produces a hormone which controls growth — of bones 

 in particular. Inadequacy in the supply of secretion leads to 

 abnormal dwarfs; exaggeration in the supply leads to abnormal 

 giants. This nanism and gigantism must be distinguished from the 

 occurrence of healthy, well-proportioned, intelligent dwarfs and 

 giants, who probably arise as germinal mutations, quite uncon- 

 nected, it may be, with anything wrong with the pituitary body. 

 In any case the pituitary body normally regulates the growth of 

 the young organism ; and there may be some fact behind the story 

 that a candidate for a cadetship, whose only defect was being an 

 inch below the standard of height, took a six weeks' course of 

 pituitary extract and succeeded in adding the required fraction 

 of cubit to his stature. Ben trovato, at any rate. It has been sug- 

 gested that some of the extinct giant reptiles suffered from pituitary 

 exaggeration; and that the elephant tribe have owed much to 

 this too. Hormones of the anterior lobe also stimulate the ovary 



