244 METABOLIC HORMONES 



of serum- calcium (G. Pickford, 1954). In Astyanax, inactivity 

 of the hypophysis resulted from maintaining the fish in darkness 

 for over 60 weeks and was associated with hypertrophy of the 

 ultimobranchial bodies (Rasquin and Rosenbloom, 1954). The 

 last example seems to be definite, even if it is thought that the 

 evidence from hypophysectomized Fundulus is not strong because 

 few fish were used, and these were apparently rather abnormal in 

 losing their ability to stand transfer to fresh water after the opera- 

 tion. Hypophysectomy does not necessarily have the latter effect 

 upon Fundulus (Fontaine, 1956). 



This association of active ultimobranchial bodies with an 

 inactive hypophysis is the reverse of the situation in mammals, 

 where the presence of TSH from an active hypophysis stimulates 

 parathyroid activity and increases blood calcium, as in the eel; 

 albeit the effect is indirectly mediated through the thyroids and 

 their power of increasing phosphates in the blood. It is possible 

 that these contradictory results may have been due to technical 

 difficulties, or to morphological differences in the hypophyses of 

 the three genera of fish concerned ; possibly the hypothalamus was 

 injured, or all parts of the hypophysis were not removed in all 

 cases (G. Pickford and Atz, 1957). Alternatively, it has been 

 postulated that the effect upon the ultimobranchial tissue may be 

 indirectly due to a hormone, ACH, of the adrenal cortex causing an 

 increase in serum phosphates (§ 5.421). ACH appears to be sec- 

 reted for some time in Astyanax in the absence of adrenocortico- 

 trophin, ACTH (§ 4.231). 



Amphibia. The most definite evidence for hormone control of 

 calcium in Amphibia is that complete removal of the parathyroid 

 glands from the bullfrog, Rana catesbmna, is followed by a fall in 

 blood calcium and eventual death from muscular tetany, much as 

 in mammals. Injections of parathyroid extract (parathormone) 

 prolonged the life of some of the frogs (Waggener, 1930). The 

 African clawed toad, XenopuSy shows seasonal variations in serum 

 calcium, the level being highest when daylight is longest; but 

 it has only been assumed, without evidence in this case, that the 

 parathyroids are active when the calcium is increased. 



It has been suggested that this seasonal control of calcium may be 

 mediated through the hypophysis in somewhat the same way as 



