744 



THE THEORY OF TRANSFORMATIONS 



CH. 



in which we may inscribe the outline of the lobster becomes a 

 shortened triangle in the case of the crab. In a little more detail 

 we may compare the outline of the carapace in various crabs one 

 with another : and the comparison will be found easy and signifi- 

 cant, even, in many cases, down to minute details, such as the 



Fig. 369. Carapaces of various crabs. 1, Geryon; 2, Corystes; 3, Scyramathia; 

 4, Paraloniis ; 5, Lujm; 6, Ghorinus. 



number and situation of the marginal spines, though these are in 

 other cases subject to independent variability. 



If we choose, to begin with, such a crab as Geryon (Fig. 369, 1). 

 and inscribe it in our equidistant rectangular co-ordinates, we shall 

 see that we pass easily to forms more elongated in a transverse 



