242 



METABOLIC HORMONES 



causes a fourfold rise in blood calcium lasting about 5 days (Fig. 

 5-26). The effect has been obtained in old crabs which would not 

 have moulted again (terminal anecdysis, Carlisle, 1957), and is 

 followed by moulting within a few weeks, if injections are repeated. 

 The same hormone appears to be responsible for moulting and for 

 Ca increase. This accounts for the earlier observations on many 

 decapods, such as Crangon, Panidirus, Astacus, Carcinus and Uca^ 

 that removal of the eyestalks increases the blood calcium ; for the 

 eyestalks contain a hormone which inhibits the action of the 

 Y-organ that lies within the head capsule. Increased blood calcium 

 leads to the formation of calcareous gastroliths, which serve as 

 stores of calcium and normally show a diurnal rhythm in their rate 



Doys ofter injection 



Fig. 5-26. Effects of an injection of an extract of Y-organ of the 

 crab, Carcinus f on the level of the blood calcium (ordinates) in the 

 same species, during the succeeding 5 days (abscissae). Black 

 circles show the effect on specimens in terminal anecdysis, when 

 they no longer moult naturally and do not secrete any hormone 

 from their own Y-organ. Open circles (below) show the lack of 

 effect of an extract of leg nerve on similar specimens (from Carlisle, 



1957). 



