Growth of Brain and A'iscera in Dogli^h 325 



The Heart. — At birth the average weight of the heart is 0.078 gram. 

 Almost from this time the increase in weight is uniform. Plate 3 shows 

 this as the only instance among the organs measured of a perfectly 

 regular increase in weight, the line of absolute weights being a straight 

 line after passing the region representing a total weight of about 170 

 grams. This means of course that equal increments are added succes- 

 sively as the total weight increases by the addition of equal increments. 

 The heaviest heart weighed 6.75 grams, showing a total increase in the 

 series of 84 times. 



The curve of relative weights is not so simple. At birth the ratio 

 is 0.11 per cent. Just after birth the heart grows more rapidly than 

 the entire organism, and this relation continues until the total weight 

 is 160-170 grams — ^double the weight at birth. This maximum ratio 

 is about 0.12 per cent, a comparative increase of about 9 per cent. (One 

 individual shows a ratio of 0.133 and two others 0.130.) From this 

 maximum the ratio decreases, at first rapidly then more slowly, until 

 in fish of average size it is only about 0.087 — considerably less than 

 at birth and about two-thirds the maximum. M with the brain the ratio 

 continues to decline steadily though slowly throughout the series, and in 

 the largest fish falls to O.OS per cent. That is, compared to the total 

 weight, the heart of the largest fish is only two-thirds as large as at its 

 maximum size or less than three-fourths as large as at birth. 



There is no distinction between the sexes in either absolute or relative 

 weight of the heart. 



The Rectal Gland. — The average weight of tlie rectal gland at birth 

 is 0.0304 gram, the heaviest weighed 1.62 grams — an increase of over 

 53 times. Between these two extremes we find, as shown in Plate 3, 

 the weights distributed along a nearly straight line much as with the 

 heart except that there seems to be a tendency among the largest speci- 

 mens for this curve to rise somewhat more rapidly. 



The curve given by the relative weights of this gland is of much the 

 same character as that of the brain, and of the heart after its maximum 

 point. At birth the ratio averages 0.0398 per cent. At first this falls 

 rapidl}^, then more slowly to a ratio of about 0.0225 in fish of average 

 size, and after this much more slowly to 0.0192 per cent in the largest 

 individual. In this specimen the rectal gland is relatively a little less 

 than one-half as large as at birth. After a weight of 2500 grams is 

 reached this curve drops scarcely at all, the line being practically parallel 

 with the base. 



