48 THE POPULAR SCIENCE MONTHLY 



at the time the report was made, while not yet sexually mature, had been 

 living in normal surroundings for six months longer than the usual 

 larval period. Evidently the prolongation of the larval period had an 

 inherited effect, and the new character was apparently a dominant 

 factor. Strangely enough no inherited effect was seen in the offspring 

 of those tadpoles which left the water before sexual maturity. Evi- 

 dently the stimulus, whatever it may be, must act on the mature germ 

 cells to produce an effect. 



Other experiments were tried on this same toad with the object 

 of changing its peculiar instinct of caring for its young. The male, 

 under normal conditions, plants the fertilized eggs on his back and 

 carries them there until the embryos have reached a stage just prior to 

 the appearance of the fore-limb buds. The tadpoles are then liberated 

 in the water. This peculiar instinct was found to be easily modified 

 by change of surroundings. 



The combined action of heat, dryness and darkness produced an 

 egg called by Kammerer " a giant egg.'" The embryo from such an 

 egg at the time of liberation was much larger than the normal type, 

 fully twice as large, with well-developed hind limbs. Upon leaving the 

 water the larva produced a small adult, a change in size due apparently 

 to lack of water in the tissues. The new form of adult laid fewer eggs, 

 which were larger and richer in yolk. Such eggs under normal condi- 

 tions produced tadpoles which, in size and form at the time of hatching, 

 were about half way between the old type and the derived type. The 

 new character, then, was partly inherited. The stimulus in this case 

 clearly did not act directly on the mature germ cells, but, if the dwarf 

 form of the adult was due to lack of water in the tissues, there may 

 have been an indirect action on the germ cells. The effect of keeping 

 the eggs enclosed in their envelopes on moist earth for a considerable 

 period of time produced a type of larva called by Kammerer " a land 

 larva." This new type when placed in the water in its usual environ- 

 ment appeared superficially like a water larva of the same age, but a 

 closer examination showed that the new conditions of development on 

 land had accelerated the growth of the lungs. The land larva had 

 lungs with well-developed air cells, while the water larva had simple 

 sac-like lungs. The inheritance of the newly acquired character was 

 evident, in that the embryos of the second generation could be kept on 

 land for a much longer period before they began to show any ill effects 

 from their unusual environment. Thus there was, according to the 

 author, a progressive adaptation to land life through the inherited 

 effects of environment. 



In the presence of a relatively high temperature, the mature toads 

 were constantly in and about the water, and in the breeding season 

 mated in the water. The egg envelopes at once swelled up, and it was 



