Growth of Brain and Viscera in Dogfish 337 



indicating that they just maintain their relative size. It is only the 

 ovaries containing large maturing ova, filled with 3'olk, that show clearly 

 the second growth cycle; this agrees with the interpretation offered of 

 their peculiar growth curve. 



Comparison with otiiek Data 



Upon attempting to consider these data comparatively w^e meet serious 

 limitations at once. The growth of the brain has been studied cpiite 

 extensively in mammals, chiefly in man (see Donaldson, '95, for refer- 

 ences) and in the guinea pig and the rat, which are typical for the 

 group, and in frogs of various species (Donaldson, '98, '03, '08, Donald- 

 son and Shoemaker, '00). Concerning the growth of the viscera we 

 seem to have no sufficiently extended data for comparative use except 

 for man, and these are not homogeneous and are far from satisfactory. 

 The data collected by Welcker and Brandt, '02, are the best, but these 

 observations are based upon such a small number of individuals that 

 their usefulness is very limited. In dealing with such variable structures, 

 records of single individuals of a given size may be very far from repre- 

 senting the actual average condition. 



The work of Donaldson ('95, '98, '03, '08) has made it well known 

 that in mammals after birth and in frogs after metamorphosis the brain 

 does not grow as rapidly as the remainder of the body, so that it becomes 

 relatively smaller as the animal becomes larger or older. Dubois. '98, 

 (this paper contains a good bibliography up to 1898), Dhere and 

 Lapicque, '98, Donaldson, '03, Beck, '07, Hatai, '08, and Eobertson, '08, 

 have proposed formulae according to which the weight of the brain can 

 be calculated quite accurately from the weight or weight and length of the 

 body or some other external characters. All of these formulae are of such 

 character as to show that in a given species the brain becomes relatively 

 smaller as the individual increases in size. To illustrate, Vierordt, '06, 

 publishes data (quoted by Donaldson, '95, from a previous edition of 

 Vierordt) showing that in human males the brain at birth composes 

 12.29 per cent of the total weight, while at 25 years of age only 2.16 

 per cent. A similar scries of data for females gave 12.81 and 2.23 per 

 cent respectively. During an increase of more than 21 times in total 

 weight the brain had increased only about 3.5 times. Welcker and 

 Brandt, '02, give a few data from several sources which show practically • 

 the same decrease. They give measurements also upon the human 



