Growth of Brain and Viscera in Dogfish 339 



fcetiis showing that at three and six months the percentage weight of 

 the brain is 20.29 and 18.74 respectively, at birth 16.10 and adult 2.42 

 per cent. 



For the bull-frog (Kana catesbiana) Donaldson, '98, gives data show- 

 ing that while the total weight is increasing from 1.32 up to 313.0 grams 

 the relative weight of the brain falls from 1.89 to 0.068 per cent. And 

 in three other species of frogs (E. pipiens, R. esculenta, R. temporaria) 

 the same author, '08, gives data showing that the brain falls from 0.57, 

 0.4G5, 0.43 per cent to 0.24, 0.24, 0.23 per cent respectively, while the total 

 weights were increasing from 11.6, 12.4, 14.1 grams to 47.0, 45.0, 32.8 

 grams respectively. We should note that in determining the total Aveight 

 ol the frogs the ovaries were included only when not pigmented, if pig- 

 mented their weight Avas subtracted. If these had been included through- 

 out, the ratios given for the large individuals would be still lower. 



And we haA'e seen that in the dogfish the brain decreased from 1,116 

 to 0.085 per cent of the total weight during growth from birth to maxi- 

 mum size. 



Obviously these figures can not be used comparatively because the 

 relative ages and conditions are so unlike, but just to emphasize the fact 

 of this universal and very considerable falling off in relative brain 

 weight these data and some others are condensed in Table I. 



The idea that the viscera, like the brain, show a relative decrease 

 during growth is perhaps less familiar. Most of the available data 

 have been collected and tabulated by Welcker and Brandt, '02, and some 

 additional data for man by Vierordt, '06. These are partially given 

 in a condensed form in Table II. In considering this table it should 

 be noted that only in the frog and dogfish are the figures the result 

 of the examination of a considerable series of specimens so that the 

 truly representative character of those included in the table is certain. 

 In the other forms often only a single individual has to serve, and when 

 we consider the great normal variability of the weight of viscera we 

 see that these figures may not give very precise information. Nor except 

 in man and the fowl have we information as to the relative size of these 

 parts at different stages of growth. In these two instances we have a 

 few scattering data given by Welcker and Brandt, '02, from their own 

 and various other sources. These data suggest that in these forms 

 more complete observations would show that many of the viscera w^ould 

 give curves showing a rise and fall as in the dogfish, but facts are so 

 scanty that nothing definite can be said on the point. Incomplete as 



