§ 5.411 BALANCE OF CALCIUM 243 



of formation in the premoult period. This could be due to diurnal 

 fluctuations in hormone secretion. 



There is some evidence that the secretion of the Y-organ is 

 under the endocrinokinetic control of Hanstrom's sensory pore 

 organ (§ 4.211). 



Insecta. There appears to be no evidence about hormonal 

 control of changes in the level of calcium in the blood of insects. 



Vertebrata. Increase of calcium in the blood of vertebrates is 

 usually attributed to the hormone of the parathyroids or their 

 equivalent structures, the ultimobranchial bodies of teleost fish. 

 The hypophysis has been shown to play a part in calcium control 

 that is neither consistent nor clearly understood ; but most recent 

 evidence seems to be against the view once held, that it supplies an 

 endocrinokinetic hormone for the parathyroids. It is more prob- 

 able that its action, at least in mammals, is indirect, through 

 secretion of thyrotrophin, TSH, that stimulates the thyroid glands 

 to secrete thyroxine (§ 4.221). This results in an increase in blood 

 phosphates, of which a high concentration stimulates the para- 

 thyroid glands to secrete their parathormone (§2.221). 



Teleostei. The ultimobranchial bodies of teleost fish are 

 embryologically comparable to the parathyroids of tetrapods ; but 

 their physiological similarity has only recently received any support 

 and is still not fully proved. Like the parathyroids their hyper- 

 trophy and histological activity is associated with decalcification of 

 the skeleton and the deposition of calcareous stones (renal calculi) 

 in the kidneys (Rasquin and Rosenbloom, 1954). It may be sup- 

 posed that this coincides with an increase in the calcium content 

 of the blood, as it would in mammals; but this has not been 

 measured in fish in relation to ultimobranchial activity. 



The hypophysis is also thought to have an effect upon the 

 calcium metabolism; but the evidence so far seems to be rather 

 inconsistent. In the eel, Anguilla^ direct measurement of the serum 

 calcium showed it to vary by 10 per cent in controls, but to drop by 

 as much as 28 per cent in 10 days after hypophysectomy (Fontaine, 

 1956). On the other hand, Astyanax and Fundulus react in the 

 opposite way, so that reduction in calcification of the skeleton and 

 formation of renal calculi are both associated with reduction or 

 loss of the hypophysis, and presumably therefore with an increase 



