82 ACQUIRED CHARACTERS SEC. 



water. It is well known that these larvae under the usual 

 conditions at a later time, while still within the mother's 

 body, lose their gills, and, what is very rare among Amphib- 

 ians, are born as completely terrestrial animals. The gills of 

 the larvae placed in water at so early an age were dispropor- 

 tionately large, and hindered the animals in their movements, 

 and in some cases they were cast off, whereupon new smaller 

 organs arose in their place. These new gills persisted in one 

 case for a surprisingly long time (fourteen weeks), and then 

 atrophied. This larva, like the rest, ultimately developed into 

 a land animal. But the remarkable fact remains that on ac- 

 count of the peculiar conditions of life artificially produced, 

 after the original gills, which were unadapted for use in a free 

 state of life, had perished, new and suitable gills were formed, 

 not in the struggle for existence against competitors with the 

 cumulative effect of selection, but, as I believe, directly from 

 purely physiological causes. These causes must, to my think- 

 ing, be sought in this, that as the pulmonary respiration was 

 not allowed to develop, and the original relations of the 

 branchial circulation therefore continued, new outgrowths of 

 the skin, i.e. gills, were formed in consequence of the unchanged 

 distribution of nutrition at the place which that distribution 

 made most favourable ; yet in the end the phylogenetic ten- 

 dency which had been for a long time established got the 

 upper hand. 



In thousands of cases, on the other hand, we are unable 

 by changing the external conditions to bring about any 

 change at all in the organism, even of temporary duration 

 the animals or plants perish rather than adapt themselves ; 

 we succeed by experiments only in killing them very rapidly. 

 It is clear that from this most simple physiological effect to 

 those of Nageli's experiments an unbroken chain of transitions 

 must exist, and that therefore the latter are in reality as 

 little surprising as the former. 



