Morphological Variation and Its Causes in A. tigriniun 71 



examined a great number of larvae. Did he by chance hit upon 

 larvae which had acquired a cannibal-dentition? Or is such a 

 dentition really universal in this species, coincident with the habit, 

 or instinct, of feeding upon large prey ? In either case, the facts 

 will prove very suggestive when compared with the instance of 

 the acquired character in A. tigrinmn. 



SUMMARY AND CONCLUSION 



From the foregoing presentation certain generalizations become 

 almost obvious, yet are worth restating. The first and chief is 

 the one with which we started, viz., the variations of A. tigrinum 

 are, primarily, acquired variations of the larva. By acquired, we 

 mean that they are the direct or indirect result of environment 

 during the larval lifetime, or, more properly speaking, during the 

 growing period of the branchiate form. The only exceptions are 

 certain sexual differences, which are not strongly marked in this 

 species, together with a few other modifications of adult structure 

 during later life. These latter are not unimportant, but are 

 mainly due to conditions that are extreme or positively unnatural 

 to the species. The capacity for variation of the young growing 

 branchiate, however, is eminently natural, being called into play 

 by changes in environment such as the species readily and in- 

 stinctively accepts. 



A second general fact, strongly apparent, is the preponderant 

 role played by nutrition in the, production of variations. Seldom, 

 indeed, is this factor negligible. The more intimate one becomes 

 through experiment and observation with the life of the species, 

 the more varied and unique become the results which are seen to 

 come from even slight nutritive differences. Even characters 

 which seem strongly adaptive and suggestive of some peculiar or 

 excessive mode of functioning, such as flattened and bordered 

 toes, excessively robust limbs, and very large gills, prove to have, 

 not only as a necessary condition but as a chief or almost exclu- 

 sive cause, an excess of nutrition. Moreover, a sudden excess or 

 deficiency of nutrition may easily determine, in several dift'erent 

 ways, the whole course of development of the animal, modifying 



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