202 



METABOLIC HORMONES 



hormone of the eyestalk (§ 5.321); but this is not shown quantita- 

 tively. Excessive water uptake cannot afford an explanation for the 

 contrary findings in Hemigrapsus, where there is no weight in- 



800 



600 - 



.o 400 - 



200 



30 40 50 60 



Carapace breodth 



70 



Fig. 5-11. Relation of the total nitrogen content of the crab, Erio- 

 cheir sinensis, to its size before and after moulting. The recorded 

 values fall into three categories, (i) Total nitrogen in body (ordin- 

 ates) measured before moulting and plotted against carapace 

 breadth (abscissae) : % for non-moulting control crabs, (ii) Total 

 nitrogen in body plus that in cast skin measured immediately after 

 moulting and plotted against carapace breadth of old shell: 

 O for control crabs moulting naturally; Q for eyestalkless crabs 

 after forced moult, (iii) Same total nitrogen as in (ii) plotted against 

 carapace breadth of neiv shell : © for controls that still fall within 

 normal range shown by curves; B foi* eyestalkless crabs after 

 forced moult due to loss of moult-inhibiting hormone, MIH. 

 These show markedly low ratios and it is assumed that though loss 

 of MIH does not affect nitrogen metabolism (ii), the loss of the 

 DIURETIC HORMONE in the eyestalk allows increased water imbi- 

 bition and swelling that increases the crab's size relative to its 

 nitrogen content (from Koch, 1952). 



crease (Table 23). Whether the abnormally large volume increase 

 observed during the first moult, following eyestalk removal in 

 Eriocheir, might be followed later by a correlated increase in tissue 

 synthesis remains to be investigated. Recent evidence on moulting 

 hormones makes a tentative interpretation of these events possible, 



