1887.1 l-J' [Claypole. 



In its native country this animal is not known to change its form but 

 hatches from the egg into a minute object much like a young tadpole and 

 gradually grows to the form and proportions of the axolotl. 



" Now in 1867 the astonishing fact was observed at the Jardin des 

 Plantes that some of these animals cast their skins after crawling out of the 

 water and began a new existence in the shape of a common salamander 

 (Amblystoma). 



"This change from axolotl to salamander is accomplished in from four- 

 teen to sixteen days and may, it seems, be always brought about in healthy 

 specimens by placing them in shallow water and gradually diminishing 

 the supply. 



"Since these axolotldescended salamanders are of precisely the same 

 species as other salamanders in the western part of the United States it 

 seems certain that these wild individuals are descended from axolotls and 

 it has been suggested that a dry season or a succession of sucli seasons 

 first caused the change to take place. If so we have here a striking 

 instance where change of climate has produced not merely another species 

 but another genus.* 



The following case given by Schmidt in his work " Descent and Dar- 

 winism " I borrow from the author last quoted. 



"At Steinheim, in Wurtemberg, was once a small lake and in its waters 

 grew countless little shellfish many of them water snails like those ot 

 lakes and rivers at the present day. By the appropriation of the lime- 

 stone dissolved in the water of the lake generation after generation ot 

 these snails built up their shells only to let them fall to the bottom on the 

 death of the little inhabitant. By this slow process a layer of shell mud 

 was formed which has, since the deposit was made, hardened into chalk. 

 About forty distinct layers of this chalk differing from one another slightly 

 in appearance may be distinguished and throughout these layers are the 

 perfectly preserved remains of many shells. The shells of each layer 

 remain much the same throughout its thickness but toward the upper 

 limit of each they are observed to vary, so as to approach the form which 

 will be found in the next layer. And not only are the shells of the lowest 

 layer so different that if the intermediate forms had not been discovered 

 they would certainly have been called different species but there are also 

 many among the intermediate forms themselves which if they had been 

 found separated from the others would have been counted distinct." 



A figure accompanies this account which exhibits the progressive change 

 from a flat, discoid, planorbiform shell at the base of the deposit to one 

 with a much elevated spire at the summit. A more striking instance of 

 invariance in monotonous conditions followed by variation on the ensual 

 of physical change can hardly be imagined, f 



* Bergen, " The Development Theory." See also Buckley's " Winners in Life's Race.' ' 

 t Mr. W. H. Edwards, of West Virginia, has recently demonstrated similar facts in re- 

 gard to several species of the Butterflies. He has shown that several forms hitherto 

 considered di.stinct are in reality only seasonal or other variates. See his "Butterflies 

 of N. America " and his numerous papers on the subject in the " Canadian Entomolo- 

 gist." 



