Growth of Brain and Viscera in Dogfish 327 



At birth the ratio of spleen weight to total weight is 0.126 per cent. 

 This ratio rises very rapidly just after birth and in fish of about 200 

 grams it reaches an average of about 0.475, that is it has nearly quad- 

 rupled. This is the most rapid initial rise observed in any of these 

 organs. The extreme variability is again shown by the range of the 

 ratios among individuals of approximately 200 grams, the limits being 

 0.257 and 0.895; this latter ratio is about six times the maximum ratio 

 found at birth. From this point the ratio diminishes gradually through- 

 out the series much as in the pancreas, falling in fish of average size to 

 0.3, and finally among the largest specimens to 0.106 per cent, or slightly 

 less than at birth and only about one-fourth the maximum average ratio. 



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

 relative weight of the spleen. 



The Liver. — The weight of the liver at birth averages 2.4 grams. As 

 with the spleen the variability of this organ is so great that the condi- 

 tion in a single specimen may differ very considerably from the condi- 

 tion shown by the examination of a large number to be typical. Plate 

 6 shows that at 8000 grams the average weight of the liver is about 365 

 grams. This would show an increase of 152 times. The liver of the 

 largest fish weighed 339.7 grams, while the heaviest liver weighed 557 

 grams, and was from a fish weighing 6811 grams. Between the extremes 

 of the series the rate of increase was seen not to be quite regular, but 

 gives a rather complex curve unlike that given by any other organ 

 examined. 



At birth the average ratio of liver weight to total weight is 3.12 per 

 cent. This rises rapidly to a primary maximum of 5.5 per cent at a 

 total weight of about 200 grams, the usual point of these maxima. It 

 then declines as usual, but ceases when about 4.2 in fish of 700-800 grams 

 and then commences to rise a second time, more slowly now, to a second 

 maximum of 7.4 per cent in fish of about 3700 grams. From this point 

 the ratio falls again until, among the six largest individuals it reaches 

 about 5.5 per cent — about the same as at the first maximum. As will 

 be pointed out later it seems possible to explain the peculiar form of this 

 curve in such a way as to show that the liver really does not differ essen- 

 tially from the other organs described with respect to its comparative 

 rate of growth. 



There is no difference between the sexes in either the absolute or rela- 

 tive weight of the liver. 



The Gonads. — At birth the gonads of the two sexes are not unlike in 

 weight either absolutely or relatively. The average weight is 0.274 



