296 ANNALS NEW YORK ACADEMY OF SCIENCES 



tral bird had a four-toed wing and, as is quite possible, that this primi- 

 tive wing was webbed, the only difference of importance between the two 

 types would be the result of different specialization, after convergence 

 had produced similar rudimentary wings, the pterosaur developing the 

 fourth toe and the bird acquiring feathers and the loss of the fourth toe. 



I think it better on the whole to keep to the well-known, if slightly in- 

 definite term "convergence" as indicating that type of evolution of which 

 we see so many examples, where from similar or even from very different 

 beginnings Nature evolves structures which closely resemble each other. 



It has been said that as a result of convergence, much of our classifica- 

 tion is unsatisfactory ; that we have grouped together in many cases ani- 

 mals which in appearance resemble one another but have arisen from 

 quite different ancestors. Doubtless there are some cases of the sort, both 

 among mammals and birds, but I am strongly of the opinion that if the 

 complete evolutionary history of every form were known, the changes that 

 would require to be made in our present systems of classification would 

 not be so very great. Such an order as the Insectivora might require to 

 be subdivided into two or more, and the Edentata also probably into three, 

 but it is very unlikely that any change of a serious nature will ever Jiave 

 to be made in such groups as the Marsupials or Monotremes or Primates 

 or Chiroptera or most others. There are always organs little liable to 

 modifications through change of habit, or which at least retain sufficient 

 tell-tale characters, such as the brain, or the organ of Jacobson, or others. 

 Some years ago, I discovered that the Elephant-shrew had an organ of 

 Jacobson quite unlike that of such a typical Insectivore as the Hedgehog, 

 and other researches since have shown good reason why Macroscelides 

 and some other forms should be removed from the typical Insectivores to 

 which they have much superficial resemblance. Among the reptiles, prob- 

 ably extremely little modification will have to be made in our classifica- 

 tion. Convergence modifies many structures, but there are always more 

 or less conspicuous characters which show the real affinity left if they are 

 but carefully searched for. 



It is impossible to discuss convergence without dealing with causes. 

 Dr. Gregory has briefly spoken of the two main theories, Darwinism and 

 Lamarckism, and has given a number of examples which would seem to 

 fit each of those rival theories. Each theory has its advocates, and many 

 of the facts of evolution are quite differently explained by the two. There 

 is at present no complete agreement on the matter, and some of the dis- 

 cussions on the subject show traces of an acrimony that recalls other 

 days. Though in the last twenty years, I have myself published close to 

 a couple of hundred papers dealing with some branch or other of evolu- 



