Growth of Brain and Viscera in Dogfish 321 



The weights of the different organs are plotted for each individual 

 separately and smooth curves derived. Each organ seems to have its 

 own rate of growth more or less independent of the others, only the 

 general features of its growth being adapted to that of the entire 

 organism. 



While the weight of the whole animal is increasing by the addition 

 of definite equal amounts the heart also increases by the addition of 

 equal increments, but the other organs, except the gonads, increase by 

 the addition of gradually decreasing increments. Peculiarity in the 

 growth of the liver is explained by the accumulation of fat in this organ. 

 Peculiarities in the growth of the gonads apparently are due to the fact 

 that at first these organs do not have a reproductive function; later a 

 second cycle of growth appears which coincides with the approach of 

 sexual maturity during which these organs are actually reproductive. 



The sexes can not be distinguished with respect to either the absolute 

 or relative weight of these parts, excepting the gonads. 



It is not the organism then, but the organ or tissue that is the growing 

 unit, the growth of the organism being a composite resultant of the 

 growth of its parts. The muscles and supporting tissues form about 

 75 per cent of the total weight, and it is chiefly the increase of these 

 parts which is measured when the weight of the total organism is taken 

 as the basis for describing growth. The growth of these predominating 

 tissues masks the differing rates of growth of parts of co-ordinate im- 

 portance though of lesser bulk and an erroneous conception of the growth 

 of organisms results. 



Comparison is made with other data and certain general conclusions 

 suggested. The muscles and supporting tissues seem to outgrow the 

 brain and viscera, a relation leading ultimately to a loss of physiological 

 balance within the organism. We should regard the condition of 

 determinate growth found in the birds and mammals as secondary and 

 as arising from the primary condition of indeterminate growth as an 

 adaptation such that the muscles and connective tissues cease their 

 growth while the more slowly growing brain and metabolizing organs 

 are still competent to carry on the work of the whole mass of the 

 organism. 



The hypothesis is suggested that the regulation of the normal growth 

 of individual tissues or organs may be carried on through specific internal 

 secretions as is known to be the case with the growth of certain occa- 

 sionally developing organs or in certain pathological growth phenomena. 

 The evidence here given is purely morphological and therefore indirect. 



