CONSTANT DIFFERENTIAL GROWTH-RATIOS 25 



mm 

 5 



.0 



I' 



I' 



10 20 



carapace breadth 



50 mm. 



Fig. 15. — Diameter of the thoracic ganglion against carapace breadth in crabs : 

 (1) Pachygrapsus ; (2) Carcinus ; logarithmic plotting. 



k in both cases about o-6. (After Teissier, 193 1 : in the original paper, the Carcinus curve is 

 erroneously ascribed to Pachygrapsus and vice versa.) 



Since the above was written, the important paper of Teissier 

 (1931) has provided numerous fresh examples. These we may 

 summarize in tabular form (and see Figs. 13-20). 



