Morphological Variation and Its Canscs in A. tigrinuin 63 



dition of these larvae becomes clear. So much energy is ab- 

 sorbed in the heroic efforts of ingestion, so much matter is re- 

 quired for the building up of the anterior part of the body and 

 of the trunk, which, to a degree, must keep pace with it, that 

 every accessory organ is reduced and all the organs are as lean 

 as possible. 



' The starvation affects mostly the gills and the limbs. Perhaps 

 actual weight constitutes the best test of these relations, and I 

 have weighed the limbs and different portions of the body upon 

 delicate balances to ascertain just what the proportions might be. 

 Thus the total weight of the four limbs of an 11 cm. cannibal 

 (preserved in formalin) is but 0.20 gr., while the limbs of a deli- 

 cate daphnid-feeder of same length weigh 0.58 gr. These figures 

 are not extreme, for by seeking among a small number of speci- 

 mens for a stronger limbed individual of equal length (also a 

 daphnid feeder) I readily find one whose limbs weigh 0.90 gr. 

 Xor is this reduction of the limbs of the cannibal merely a matter 

 of general emaciation, as is shown by the ratio of the weight of 

 the limbs to the entire weight of the animal. The weight of the 

 limbs of the above young cannibal constituted a little less than 

 one sixty-fourth of its entire weight, while with the second speci- 

 men they constituted one twenty-first, and in the third somewhat 

 less than one-sixteenth. Even more striking would have been the 

 discrepant relations had I chosen the posterior limbs alone for 

 comparison. In all ordinary larvae the posterior limbs are larger 

 and heavier than are the anterior. Not so with these young can- 

 nibals. So strongly is the development shifted to the anterior 

 end in these animals that the relative sizes of the limbs are quite 

 reversed ; the anterior limbs, though very slender, remain about 

 normal in length, while the posterior are reduced in both length 

 and girth. To illustrate thus these more extreme contrasts : the 

 weight of the posterior limbs of the above young cannibal (0.09 

 gr. ) was contained in the total weight nearly one hundred and 

 forty-three times, while in the heavier-limbed pond larvae of the 

 same length, the weight of the posterior limbs (0.50 gr.) entered 

 into the total weigfht a little over twentv-nine times. 



?59 



