320 William E. Kellicott 



the animal body, and that the growth of one or two bulky tissues has been 

 mistaken often for the gro^Yth of the organism. Further, some of the 

 problems of growth have been overlooked because of the failure to bear 

 in mind the ph3'siological distinction between determinate and indeter- 

 minate growth among animals. The birds and mammals are unusual 

 among vertebrates in that they continue to live for a long time after 

 maturity without continuing to grow meanwhile. This is certainly true 

 of man and seems to be true of the other mammals ; and yet the mam- 

 mals are the forms whose growth has been studied most extensively and 

 from which many fundamental conceptions of growth have been derived. 

 The problem of growth is somewhat different among all of those lower 

 forms wdiose growth is indeterminate and continues, though slowly 

 to be sure, throughout life, and which represent a more primitive con- 

 dition in this respect. The present paper presents a fairly complete 

 series of data regarding the increase in weight of the brain and certain 

 of the viscera in a form which grows indeterminately, and suggests a 

 possible interpretation of their significance for the general problems of 

 growth. 



SuM:\rARY 



A series of 315 dogfish (Mustelus canis) including specimens from 

 birth (length 32.8 cm., weight 7G.2 grams) up to a female 135.1 cm. in 

 length, weighing 8434 grams, has been examined with a view toward 

 getting precise information regarding the relative growth of the brain 

 and viscera. Accurate w^eighings were made of the brain, heart, rectal 

 gland, pancreas, spleen, liver and gonads. It is found that these viscera 

 as well as the brain are relatively largest in the smaller individuals and 

 that they decrease in size relatively throughout life although they do 

 not cease to increase in actual weight. The period of maximum relative 

 size of these parts is about that at which the growth of the whole organism 

 is most rapid. 



While the ages of these fish can not be determined exactly it seems 

 that the dogfish of one meter in length, weighing approximately 2750 

 grams, is probably about five years old. Females are not ordinarily 

 mature before this size is reached, although the males may mature con- 

 siderably before this. Absence of the time factor in these observations 

 is not important because their factors, such as food and temperature, 

 are known to be of more importance than age in determining the size 

 of fish. 



