330 William E. Kellicott 



year this relation is reversed. Probably the actual average weights and 

 lengths at different ages would be found to differ somewhat from these 

 figures, but this is the best approximation I can make with the avail- 

 able data. This is precisely the type of distribution which has been 

 found repeatedl}' in the measurement of teleosts. (See, for example, 

 Moenkhaus, '95, and Fulton, '01, '06). 



It is undoubtedly true that here, as in the teleosts observed, age is 

 not the chief factor in determining size, but that, as in so many inver- 

 tebrates, the factors of food and temperature are the most important. 

 Therefore to relate total size with age in these and similar forms would 

 not add much to the interpretation of these size relations. As affecting 

 the size of the brain and viscera probably the age is of still less impor- 

 tance, so that for these organs we are upon a more instructive basis in 

 considering their weights as compared with that of the entire organism 

 without reference to age. Consequently the absence of a known time 

 factor is not the serious matter it might seem at first thought or prob- 

 ably would be were we considering a higher vertebrate such as a bird 

 or mammal. 



As compared with these curves in which total weight irrespective 

 of age is alone the basis of comparison, the curves given by the time 

 rate of increase would differ in their precise form, since different lengths 

 of time would be required to cover what are here indicated as equal 

 distances along the base line. If the time element could be introduced 

 the curves would probably be shortened chiefly in the region between the 

 total weights of 1000 and 2000 grams and somewhat less below and above 

 these weights, and then lengthened considerably from the middle part 

 onward. 



Considering in the first place, then, the absolute weights of the organs 

 measured, we find, first, that while the curves are all of essentially the 

 same character, yet, second, each is distinguished by certain details of 

 form, and, third, excepting only the liver and gonads, they are all of 

 simple character with no indication of being formed by two or more 

 dissimilar elements or cycles. No attempt has been made to describe 

 any of these curves mathematically. With the exception of the curve 

 of gonad weights which is obviously of special character, it is possible 

 to arrange the curves in a series between the members of which the 

 differences are minimal. 



Commencing with the spleen (Plate 5) we have a curve which is 

 distinctly concave to the base line throughout its entire course, al- 



