Chap. IV. MANNER OF DEVELOPMENT. 151 



to the os coccyx, which in man and the higher apes 

 manifestly consists of the few basal and tapering seg- 

 ments of an ordinary tail, I have heard it asked how 

 could these have become completely embedded within 

 the body ; but there is no difficulty in this respect, 

 for in many monkeys the basal segments of the true 

 tail are thus embedded. For instance, Mr. Murie in- 

 forms me that in the skeleton of a not fall-grown 

 Macacus inomatus, he counted nine or ten caudal ver- 

 tebrae, which altogether were only 1*8 inch in length. 

 Of these the three basal ones appeared to have been 

 embedded ; the remainder forming the free part of the 

 tail, which was only one inch in length, and half an 

 inch in diameter. Here, then, the three embedded 

 caudal vertebras plainly correspond with the /our coal- 

 esced vertebras of the human os coccyx. 



I have now endeavoured to shew that some of the 

 most distinctive characters of man have in all proba- 

 bility been acquired, either directly, or more commonly 

 indirectly, through natural selection. We should bear 

 in mind that modifications in structure or constitution, 

 which are of no service to an organism in adapt- 

 ing it to its habits of life, to the food which it con- 

 sumes, or passively to the surrounding conditions, can- 

 not have been thus acquired. We must not, however, 

 be too confident in deciding what modifications are of 

 service to each being : we should remember how little 

 we know about the use of many parts, or what changes 

 in the blood or tissues may serve to jit an organism for 

 a new climate or some new kind of food. Nor must 

 we forget the principle of correlation, by which, as 

 Isidore Geoffroy has shewn in the case of man, many 

 strange deviations of structure are tied together. Inde- 

 pendently of correlation, a change in one part often leads 



