Growtli of Brain and Viscera in Dogfish 341 



tlie data are they represent the state of our knowledge and are given 

 in the table for what they are worth. 



The net result is to show that among the vertebrates generally the 

 parts which increase relatively the most during growth are the skeleton 

 and muscles and perhaps the skin and subcutaneous tissue. Together 

 these make up roughly three-fourths of the total weight. The viscera 

 as well as the brain show a falling off at various rates. 



Conclusion 



We see then that it is a general law among vertebrates that the organ- 

 ism does not grow entirely as a unit but as the resultant of the growth 

 of its parts, and that these component parts of the body do not all grow 

 at the same or corresponding rates. What is ordinarily measured and 

 described as growth of tbe organism is really not growth of the whole 

 organism, but the growth chiefly of the locomotor, supporting and pro- 

 tective tissues, and probably frequently of fat also. The curve of 

 growth of an organism is a composite affair made up of many dissimilar 

 components, with the growth of those mentioned as the predominating 

 elements. Such curves therefore may be misleading unless this rela- 

 tion is borne in mind, since disproportionate importance is thus allowed 

 to elements of the body which should be considered of only co-ordinate 

 importance. Indeed it is not clear why, in the growing organism, the 

 condition of the brain and viscera should not be the more significant, 

 and 5^et the growth of these parts is almost completely masked by the 

 increase of the bulkier muscles, skeleton and skin. 



It seems that some confusion has arisen in the study of growth through 

 the failure to remember that in all of those forms whose growth has been 

 studied most extensively, growth is determinate: the organism reaches, 

 about the time of sexual maturity, a fairly definite average size, then 

 stops growing and may continue to live for a considerable time there- 

 after. This is true for mammals and birds at least and perhaps also 

 for some of the lower vertebrates. In some forms the organism or 

 parts of it may actually diminish in weight. But among fishes quite 

 another condition prevails: growth is indeterminate and the fish may 

 continue to increase in weight, slowly it is true, as long as it remains 

 alive, with an average food supply. This seems to be the condition 

 among most invertebrates, except insects, and has been demonstrated in 

 the teleost fishes (Fulton, '01, '06), and from these data it must be true 



