402 SCIENCE PROGRESS 



Now, Kammerer asserts that, if S. atra be gradually accus- 

 tomed to live under warmer and moister conditions, she will 

 begin to produce first three and ultimately four young at a 

 birth, that these young will enter the world at an abnormally 

 early period of development — even before the gills are fully 

 absorbed ; that if these young be reared to maturity under 

 the same conditions, they will give rise to still more young at 

 a birth, and these young will be provided with gills, and will 

 take to the water — in a word, that S. atra can be induced to 

 assume the habits of S. tnaculosa, and that these habits will be 

 transmitted to posterity. 



Some of Kammerer's critics, while accepting this result, have 

 maintained that it is not a genuine case of the inheritance of 

 acquired characters, because the habits to which S. atra reverts 

 under the influence of more favourable conditions are the ances- 

 tral habits of the race. But this objection involves a confusion 

 of thought. When a habit and the structures associated with it 

 have completely vanished, if by exposure to different conditions 

 the old habit is reacquired, and descends to subsequent genera- 

 tions, the case is just as genuine an instance of the inheritance 

 of an acquired character as if the new character were one totally 

 foreign to the past experience of the race. It is a superstition to 

 think that evolution is bound to go forward ; it may go back- 

 ward as well. But Kammerer has a neat way of outflanking 

 this silly objection. He has performed the reverse experiment. | 

 If S. maculosa be subjected to conditions of increasing cold and " 

 dryness, it produces fewer at a birth, and these are born in a more 

 advanced stage of development. In three generations a state 

 of affairs is reached when only three to four are born at one 

 time, and in these the gills are mere stumps, the gill clefts 

 closed, and the animals can at once take up their life on land ; 

 in a word, S. maculosa has acquired the habits of S. atra. Now, 

 if S. maculosa be taken as representing the ancestral condition 

 of S. atra, S. atra cannot be ancestral to S. maculosa. 



Another experiment of Kammerer's which has raised an 

 enormous amount of discussion has for its subject the midwife 

 toad Alytes obstetricans. Most toads, though they spend 

 a good deal of their time on land in cool damp spots, nevertheless 

 resort to the water in order to pair. Here the male embraces 

 the female round the waist, maintaining his hold on her by 

 means of a roughened horny pad situated on the ball of the 

 apparent thumb. (The real thumb is absent ; the apparent 

 thumb is the modified index finger.) After a period of sexual 

 enjoyment which may extend over weeks, the female emits 

 the eggs, which issue from her in two long strings, held together 

 by a clear jelly-like substance. As the eggs appear, the male 

 fertilises them by emitting the spermatozoa ; the fertilised 



