xxxviii INTRODUCTION 



kind of evolution above described could not possibly account 

 for all the varied shapes of existing animals. The series is 

 full of anomalies. Birds, for instance, are lower in the 

 scale than mammals. Yet their pectoral muscles and 

 sternum are developed out of all proportion to their proper 

 place in the series. Then, again, whales have no legs ; yet 

 legs reappear farther down the series, for birds have them, 

 and so do many reptiles, not to speak of lower animals. 

 If evolution was solely as hitherto described, we should 

 expect legs to vanish gradually as we passed down the 

 scale ; and having vanished, not to reappear again. 



Within a single class, such as reptiles, the same anomaly 

 is seen. Frogs (for Lamarck included amphibians with 

 reptiles) breathe by gills when first born : hence they are 

 inferior to snakes which never have anything but lungs. 

 Yet snakes have no legs, while frogs have legs : that is to 

 say, the lower animal is better oif for legs than the higher. 

 Whence these numerous anomalies ? It is to Lamarck's 

 solution of this problem that we must now turn our attention. 



§ 5. Inheritance of Acquired Characters. 



Acquired modifications, as distinct from the so-called 

 spontaneous variations, are of two different kinds. In the 

 first place, there are those modifications which are due to 

 the direct action of the environment, without reference to 

 any active efforts on the part of the organism. Such, for 

 instance, are various modifications in colour, etc., of the 

 superficial layer of the body, due to the application of light 

 or heat : such, again, are mutilations. In the second place, 

 there are those modifications which arise from the greater 

 or lesser use of any part, due to some environmental cause, 

 which requires the organism to exert certain parts to a 

 greater or lesser extent than the average. This latter type is 

 referred to as functionally-produced modifications, and their 

 inheritance is often called use-inheritance. It is this latter 

 type alone that Lamarck regarded as being a factor in 



