Conditions governing deposition of eggs 269 



Kammerer has investigated the conditions for the laying of eggs in 

 two forms of salamanders, e.g. Salamandra atra and & maculosa. 

 In both forms the eggs are fertilised in the body and begin to 

 develop in the uterus. Since there is room only for a few larvae in 

 the uterus, a large number of eggs perish and this number is the 

 greater the longer the period of gestation. It thus happens that 

 when the animals retain their eggs a long time, very few young ones 

 are born ; and these are in a rather advanced stage of development, 

 owing to the long time which elapsed since they were fertilised. 

 When the animal lays its eggs comparatively soon after copulation, 

 many eggs (from 12 to 72) are produced and the larvae are of course 

 in an early stage of development. In the early stage the larvae 

 possess gills and can therefore live in water, while in later stages 

 they have no gills and breathe through their lungs. Kammerer 

 showed that both forms of Salamandra can be induced to lay their 

 eggs early or late, according to the physical conditions surrounding 

 them. If they are kept in water or in proximity to water and in 

 a moist atmosphere they have a tendency to lay their eggs earlier 

 and a comparatively high temperature enhances the tendency to 

 shorten the period of gestation. If the salamanders are kept in 

 comparative dryness they show a tendency to lay their eggs rather 

 late and a low temperature enhances this tendency. 



Since Salamandra atra is found in rather dry alpine regions 

 with a relatively low temperature and Salamandra maculosa, in 

 lower regions with plenty of water and a higher temperature, the 

 fact that S. atra bears young which are already developed and 

 beyond the stage of aquatic life, while S. maculosa bears young ones 

 in an earlier stage, has been termed adaptation. Kammerer's experi- 

 ments, however, show that we are dealing with the direct effects 

 of definite outside forces. While we may speak of adaptation when 

 all or some of the variables which determine a reaction are un- 

 known, it is obviously in the interest of further scientific progress 

 to connect cause and effect directly whenever our knowledge allows 

 us to do so. 



VII. Concluding Remarks. 



The discovery of De Vries, that new species may arise by muta- 

 tion and the wide if not universal applicability of Mendel's Law 

 to phenomena of heredity, as shown especially by Bateson and his 

 pupils, must, for the time being, if not permanently, serve as a basis 

 for theories of evolution. These discoveries place before the experi- 

 mental biologist the definite task of producing mutations by physico- 

 chemical means. It is true that certain authors claim to have 



