Ill] OF UNEQUAL GROWTH OR HETEROGONY 209 



From the observed data we may solve, by the method of least 

 squares, the simple equations 



y = a -{- bx, z= c + dx, 



or in other words, find the equations of the straight lines in closest 

 agreement with the observed data. The solutions are as follows*: 



y - 11-02 + 0-512^, and z^- 5-64 + 0-368x, 



the two coefficients 0-368 and 0-512 signifying the difference between 

 the rates *of increase of the two organs. The number of samples is 

 not very large, and some deviation is to be expected; nevertheless, 

 the calculated straight lines come close to the observed values. 



40 



10 



20 



Fig. 



30 40 50 



Total length (mm.) 



55. Relative growth of body and mandible in reindeer-beetle 

 {Cydommatus tarandus). 



The reindeer-beetle {Cydommatus tarandus), belonging to the 

 same family, shews much the same thing. The mandible grows in 

 approximately linear ratio to the body, save that it tends to be at 

 first a little above, and later on a little below, this Unear ratio 

 (Fig. 55). 



Measurements o/ Cydommatus tarandus f (mm.) 



* As determined for me by Dr A. C. Aitken, F.R.S. 



t Data, much abbreviated, from Huxley, after E. Dudieh, Archivf. Naturgesch. (A), 

 1923. 



