88 THE POPULAR SCIENCE MONTHLY. 



evolution be true, and which, therefore, are upon the whole strongly 

 in favor of the doctrine of development. He makes a number of ad- 

 missions. He allows that there are species which have continued un- 

 changed, not only throughout all historical years, but all geological 

 ages. Cuvier has shown that the ibises, dogs, and cats depicted 3,000 

 years ago or more on the monuments of Egypt are the same as those 

 found in that country in the present day. The professor mentions a fish 

 of the chalk formation named cericus, which is represented at the pres- 

 ent day by a very closely-allied species living in the Atlantic and Pa- 

 cific Oceans. He thence argues that there is no intrinsic necessity in 

 animal forms to change and to advance, as some sciolists assume. But 

 he labors to prove that there are cases in which varieties have be- 

 come species by reason of being suited to their surroundings. He gives 

 credit to Mr. Darwin for bringing in two great factors in the process 

 of evolution : " One of them is a tendency to vary, the existence of 

 which may be proved by observation in all living forms ; and the 

 other is the influence of surrounding conditions upon what I may call 

 the parent form, and the variations which are thus evolved." He 

 adds : " The production of variations is a matter not at all properly 

 understood at present. Whether it depends on some secret machinery 

 if I may use the phrase of the animal form itself, or whether it 

 arose from the influence of conditions upon that form, is not certainly 

 a matter for our present purpose.*' True, this may not be for the 

 purpose of his lecture, but it must be cleared up before we can clear 

 up the subject of development. The nature and laws of variations 

 and the peculiar laws of heredity are at present shrouded in mys- 

 tery. When we know more of them and of the forces at work, we 

 shall be in a better position to determine whether varieties ever do 

 become distinct species. 



The professor acknowledges that geology does not furnish decisive 

 evidence of one form of life passing into another. But then he claims 

 that the geological record is not complete; that much of what is 

 written in stone has been effaced, and that if it were complete it 

 would show us the missing links. To equal him in candor I admit 

 that transitional forms are ever casting up. He shows that in cer- 

 tain fields we have those transitions already disclosed. He dwells on 

 the resemblances and the affinities between reptiles and birds, and 

 refers to animals which have some of the properties of both. Thus 

 there are birds that have teeth, and reptiles that have wings and can 

 stand on their two hind-legs, such as the hadrosaurus found in New 

 Jersey. His demonstration, as against Owen, seems to me complete 

 here. True, there are naturalists who maintain that the teethed bird 

 is still a bird, and the archeoptrix a reptile, a variety and not a tran- 

 sitional form. Still, such cases indicate a tendency on the part of the 

 reptile to rise to the bird, and of the bird to retain properties of the 

 reptile ; and natural selection and development alone can explain this. 



