REGIONAL GROWTH 



93 



The most clear-cut examples concern the abdomen of crabs, 

 which in all cases are narrow in the male, broadly expanded 

 in the female. A large series of measurements has been made 

 by Sasaki (1928) on both sexes of the Japanese species Tel- 

 messus cheiragonus. Analysis of these data shows that whereas 

 the growth-gradient for breadth in the male abdomen is nearly 



2.5 



© 



id 

 4) 



a 



"aS-d 2.0 



s — 

 .2 a. 



4J 



1.3 



o 

 u 



O 



3 4 



Segments of abdomen: distal — > 



Fig. 52. — Growth-gradients in the abdomen of crabs. 



Solid lines, for breadth of abdominal segments: ©, Telmessus cheiragonus, <$ ; X, Telmessus 

 cheiragonus, 9 : +, Pinnotheres pisum, $. Dotted line, for length of abdominal segments in 

 Pinnotheres pisum, ? . 



flat, with its growth-centre, if so it may be called, near the 

 centre of the region, in the female it is steeper, with its centre (as 

 in the typical male chela) in the penultimate segment (Fig. 52). 

 These figures may be compared with those cited for the 

 edible crab, Cancer pagurus, by Pearson (1908, p. 21) in two 

 large specimens of the same size but opposite sex (Table IX). 



TABLE IX 



Cancer pagurus; from data of Pearson, 1908. 



