Morphological J^ariation and Its Causes in A. tigrinum 55 



breeding places of the species in my vicinity. Si.vtJi, among hun- 

 dreds of larvae raised by me this type never appeared, with the 

 possible exception of a single cistern-grown specimen. This in- 

 dividual did show many of the characters of the broad-heads and 

 was equally vicious, laying hold of a stick with which I gently 

 touched its tail to see if it were dead — so long did it remain un- 

 moved upon the bottom — with a violence utterly unamblystoma- 

 like. Seventh, specimens of this type and even transitional forms 

 approaching it only were always larger than the other larvae of 

 the same year accompanying them, sometimes very much larger. 

 Eighth, despite this rapid growth many of these specimens, espe- 

 cially the more extreme ones, showed unmistakable signs of un- 

 dernutrition. Several, indeed, were more emaciated than any 

 other larvae I had ever taken under natural conditions. Not only 

 were the bodies shrunken, but the back-fins had the form indi- 

 cating semistarvation, and the very small gills were, as my ex- 

 periments at this time were demonstrating conclusively, also the 

 products of undernutrition. Only among the transition types did 

 certain individuals appear well nourished, large gilled, etc.. such 

 as figure i, plate IX. Even these were in the decided minority. 



These last facts, rapid growth and large size, together with all 

 the signs of undernutrition and even starvation, would have 

 seemed too impossible for belief had not the age, etc., of the 

 specimens been positively known to me. They offered, however, 

 no clue to explanation. Certain of the other facts, however, did 

 suggest to me the possibility that the form was due to some spe- 

 cial habit of feeding, possibly to the habit of cannibalism. I tried 

 the effect of feeding certain larvae upon very large pieces of 

 meat, but the larvae either refused the food or killed themselves 

 in swallowing it, or, more frequently, were thrown into early 

 metamorphosis by the irregular nutrition. 



Not until June, 1903, did I secure more adequate material and 

 further evidence as to the nature of the variation. At the early 

 cleaning of the reservoir, on the 15th of June, I discovered that 

 the number of young amblystomas present was several-fold the 

 usual content of the place, probably five thousand were present, 

 and among the fifteen himdred which I secured of the largest 



251 



