514 FREDERICK S. HAMMETT. 



suggestive of a greater interdependence or dependence on a 

 common factor. Body weight and body length are thus more 

 closely related in differential development, than is the brain or 

 spinal cord related to either of them individually. That is to 

 say, body weight and body length follow more nearly parallel 

 courses during differential development than do brain and body 

 weight or body length, and spinal cord and body weight or body 

 length. The difference can be attributed to the probability that 

 the type metabolism productive of body weight is more nearly like 

 that productive of body length, than is the type metabolism of 

 body weight and body length like that which characterizes brain 

 and spinal cord. In the case of body weight and body length 

 the reactions are essentially increments in protoplasm, in the 

 case of the brain and spinal cord the differential development is 

 characterized by lipoid accretions. 



The correlation between brain weight and body weight (n 3 ) 

 is less than that between the other pairs of variables with the 

 exception of brain weight and body length (r 2 3). The degree of 

 difference is valid in 50 per cent, of the cases. The difference if 

 accepted as significant is suggestive of a lesser dependence of 

 brain weight and body weight on a common factor. That is to 

 say brain weight and body weight are less related in differential 

 development than are spinal cord weight and body weight and 

 length, and than brain weight and spinal cord weight with each 

 other. From which it can be inferred that during differential 

 development brain weight deviates more from the course followed 

 by body weight, than it does from that followed by the spinal 

 cord, or than does the spinal cord deviate from the course 

 followed by body weight and body length. 



The greater association between brain and spinal cord (r s 4 ) is 

 undoubtedly due to the community of type metabolism as com- 

 pared with the disparity between brain and body weight. The 

 higher degree of association between spinal cord and body length 

 (r z 4) is justly attributed to the structural relations existing in 

 this case. Why cord weight should be more closely associated 

 with body weight (rz 4) than is brain weight is a question. It 

 may be that the preference is a consequence of the structural 

 relationship of the cord with the body length of high degree of 

 correlation with body weight. 



