INHERITANCE OF ACQUIRED CHARACTERS. 447 



he can at intervals dip his legs, and if the eggs are kept wet 

 enough the embryos eventually emerge into the water, biting 

 their way out of the egg-shells by their horny beaks. Their 

 post-embryonic development lasts more than a year. 



Now, if Alytes is kept at a temperature of from 25° to 30° C, 

 the male draws the eggs out of the cloaca of the female, but does 

 not wind them round bis legs. If this happens on land the ad- 

 hesion is prevented by the rapid drying up of the jelly, but it more 

 often happens in the water, since the heat causes the Toads to 

 forsake their usual habits and cool themselves in the water, and 

 here the adhesion is prevented by the rapid swelling of the jelly. 

 The movements of the embryo inside the egg are sufficient to 

 effect the disruption of the membrane, which is macerated by this 

 swelling in the water, and the embryos escape after two weeks 

 at a very early stage with a yolk-sac still attached to them, and 

 long delicate, vascular embryonic gills. These gills are soon 

 replaced by others adapted for respiration in the water. The 

 post-embryonic development only' lasts three to four months, 

 and the resulting Toads are exceptionally large. 



After a time the adults become accustomed to copulating in 

 the water, and seek it for the purpose even when kept in normal 

 conditions. They then produce from ninety to one hundred and 

 fifteen small eggs with little yolk. This is soon absorbed, and 

 the embryos, impelled by hunger, jerk violently about till they 

 break out of the egg. Since they are not encumbered by a yolk- 

 sac, as were those of earlier broods, they can swim freely at once, 

 and to this end their tail-fins are distinctly broader than in the 

 tadpoles derived from earlier broods. The gills also become 

 more readily adapted to aquatic respiration. The Toads derived 

 from the earlier broods reared in the water lay their eggs on land 

 in the normal fashion if the experimental conditions are relaxed. 

 Those derived from the later broods, however, after spawning in 

 the water has become habitual, show that they inherit this 

 tendency by always spawning there, even without continuance 

 of the conditions. 



If the high temperature is still maintained, the eggs produced 

 by this second generation are still smaller and more numerous 

 than in those of the first, and if the process is still continued the 

 larvse in the fourth generation are darkly pigmented instead of 



