M. W. Veltmaim on the Descendence-Theory. 417 



LI. — The Descendence-Theory considered from some special 

 points of view. Bj W. Veltmann*. 



Deviations from the average constitution of tlie species may 

 be advantageous to the individuals and, according to Darwin's 

 view, may induce the production of new species by natural 

 selection in five different ways : — 



1. From birth a longer duration of life. Here that duration 

 of life is meant which is attained by the animal when it dies 

 a natural death, after existing during its life under normal 

 conditions. The greater this duration of life pertaining to 

 the animal in accordance with its original constitution, the 

 greater also, on the average, will be its actual duration and, 

 consequently, the assistance given by it to the maintenance of 

 the species. 



2. Easier nourishment, /. e. attainment of the necessary 

 food. In connexion with the inheritance of peculiarities this 

 comes into consideration, inasmuch as deficiency of nom'ishment 

 is prejudicial to the development and activity of the sexual 

 system, and may also abridge the duration of the time of 

 rejjroduction, and even life itself. 



3. The faculty of more easily escaping pm'suers and other 

 dangers. In this, greater protectedness of the eggs and young 

 from destruction is included. 



4. Greater facility of efiecting copulation (clasping, seizing 

 the female, &c.). 



5. Greater fertility. 



Among these various momenta, 2, 3, and 4 depend in part 

 upon the stronger and more persistent constitution of the in- 

 ternal organs ; but 1 is also dependent upon this. But 2, 3, 

 and 4 are conditional upon the production of special internal 

 and external organs or other properties (colour &c.). The 

 differences in participation in propagation hereby produced, as 

 also those in connexion with 5, may, however, always be very 

 small, as very considerable deviations always occur very 

 rarely and quite isolatedly. The differences in congenital 

 duration of life are, on the contrary, very considerable. These 

 will therefore always have so predominant an influence, that 

 that of the other casual deviations disappears before it. It 

 follows from this that from a species no other species possess- 

 ing a shorter period of life can be produced. Of all deviations 

 in the external or internal constitution, only those can become 

 constant which tend to a longer period of life. 



Differences in fecundity could only have an equal degree of 



* Translated from the 'Archiv fiir Naturgeschichte,' Jahrg. xxxvi. 

 pp. 236-246, by W. S. Dallas, F.L.S. 



