ADAPTATION AND INHERITANCE KAMMEREK. 431 



toad (Alytes ohstetricans) . In order to understand this, it becomes 

 necessar}^ to say a lew words about the ordinary method of reproduc- 

 tion in most of the toads and frogs (fig. 8). They deposit their small 

 eggs, hundreds in number, in water. The eggs are surrounded by a 

 jelly-like substance that unites them into bunches or strhigs (fig. 8a). 

 Here the jelly-like covering swells at once about each dark-colored 

 egg as a sharp ly-diiTorcntiated translucent ball (1&). The eggs remain 

 without attention from the parents after deposition. The young (c) 

 escape from the eggs. The free larvae, so-called tadpoles, which at 

 first are not provided with any special breathing apparatus, for they 

 breathe with the outer skin (d), develop external gills after a few 

 days (e), which are later retracted (/) and give way to inner gills (t). 

 But still for weeks the larva remams witliout feet (Ii). It develops 

 first the posterior (i), then the anterior extremities (k, I), after which 

 the tail becomes shriveled and the narrow, horny jaw is replaced 

 by the deeply cut mouth of the frog (in). Then the small complete 

 frog jumps to land. 



There is only a single exception to this rule in Europe, the so-called 

 midwife toad, or egg-bearing toad (fig. 9). In this the deposition of 

 eggs takes place on land and a comparatively small number of eggs 

 (18-83) are produced, but which, on account of their great yolk mass, 

 appear large and light colored (fig. 9, 2a). The jelly capsules which 

 connect these eggs into a chain can not swell in the air, but, on the 

 other hand, become contracted and fit closely to the surface of the 

 egg. The male assists the female during oviposition by drawing 

 the string of eggs from the cloaca. He also assists in the brooding 

 of the eggs (comp. fig. 10, 7 <? ), winding the eggs about his thighs and 

 carrying them about in this manner, until the young are ready to 

 emerge. At this time the male with his burden enters the water, 

 where the larvjB break their ca]:)sules. They do this not in the stage 

 unprovided with special breathing organs, for this and the following 

 stage, that with external gill, are passed over in the egg. The larva 

 is still footless (fig. 9, 2h), but has internal gills. The succeeding 

 developmental stages agree with those of other frogs and toads — two- 

 legged (2c) , four-legged (2-d), shriveling of the tail, and habitat change 

 from water to land in the completed toad (2e). 



I was able to change the above-mentioned process considerably in 

 four directions. In the first, the aquatic existence of the larva was 

 much prolonged (fig. 9, the detail fig. 6). I gradually learned to what 

 extent factors like darkness, cold, richness of oxygen hi the water, 

 overfeeding after previous starvation, and the early removal of the 

 embryo from the egg, played in prolonging the metamorphic period 

 of the toad. With each one ot these factors I obtained larvae which 

 did not transform at the proper time, and which already in the larval 

 stage attained considerable size, still, what is most important, 



