INHERITANCE OF ACQUIRED CHARACTERS 49 



impossible for the male to plant these " water eggs," as the author calls 

 them, on its back. Therefore the early stages developed in the water 

 as is the case with other amphibians. The habit of mating in the 

 water became fixed, and persisted after the removal of the artificial 

 conditions of temperature. The eggs, meantime, at each successive 

 laying became smaller and smaller through the loss of yolk. The larvae 

 hatched at a much younger stage than the larvae from normal eggs. 

 The adults reared from the water eggs mated in the water at the first 

 breeding season, even under normal conditions of temperature. Suc- 

 ceeding generations showed intensification of the new characters in the 

 decrease of yolk, and also in the development of more gills, which 

 changed in number from one pair to three pairs. There was, therefore, 

 as in the preceding case, an apparently progressive adaptation to 

 environment through the inheritance of acquired characters. 



The effect of this change on the germ plasm was tested by a cross 

 between the old type and the derived type. The new character, as 

 judged by the instinct for mating in the water, behaved like a dominant 

 Mendelian factor. Dominance, however, was of an unusual kind. The 

 male, whether of the old or the new form, impressed its character on 

 all the offspring of the first generation, but the second filial generation 

 showed the usual kind of segregation of characters in the ratio of three 

 individuals of the dominant form to one of the recessive. Clearly the 

 unexpected feature in the behavior of the factors in this crossing lies in 

 the peculiarity of the sex-limited potency, not in the isegregation of fac- 

 tors. The most interesting fact in the experiment is the attempt to 

 prove a change in the germ plasm by the modern method of applying 

 the test of cross breeding. 



Another series of experiments was tried on the tree frog, Hyla. 

 This frog lays its eggs in the water in bunches of 800-1,000, enveloped 

 by the usual coats of gelatine. A number of frogs were kept away 

 from the water, but were allowed to crawl about on a water plant which 

 held small amounts of moisture in the bases of its leaves. During the 

 mating season the frogs deposited their eggs in the moisture on the 

 leaves, according to a habit which is common among some of the tropical 

 representatives of the genus. The young remained in their envelopes 

 until the gills had become enclosed, whereas the young under normal 

 conditions begin a free swimming life before the gills appear. A new 

 type of adult was produced marked by its small size. These dwarfs 

 when reaching maturity laid their eggs in water after the usual manner. 

 The new habit was not inherited. The offspring of the dwarf frogs, 

 however, had external gills at the time of hatching, a stage half way 

 between the old and the derived type, and, moreover, they grew into 

 adults of a size half way between the two types. This experiment, 

 therefore, showed results very similar to those shown by the experiment 

 on Alytes. 



VOL. LXXXII. — 4. 



