GEOGRAPHICAL DISTRIBUTION AND DESCENT. 



95 



other places remains of small animals, in some 

 cases as large as foxes, which were formerly 

 referred, under the name of Adapis, to the 

 Ungulata, but which, on careful examination, 

 exhibit such close affinities to the Prosimii 

 that a controversy is still carried on between 

 the finders as to whether they must be 

 referred to the one group or the other. 

 These remains include some almost entire 

 skulls ; and this uncertainty at any rate shows 

 that we have here to deal with transitional 

 forms, whose relations are all the more diffi- 

 cult to determine since they occur along with 

 the remains of genuine Prosimii, and accor- 

 dingly cannot be the ancestors of the latter. 



In North America the case is the same. 

 Wyoming has yielded a large number of such 

 transitional forms, which have been called 

 Limnotherida; but besides these a small 

 number of other forms, Lemuravida, which 

 show much closer affinities to the lemurs. 



Neither in the Old nor the New World 

 have there yet been found in later strata 

 any remains which can be shown to belong 

 to the Prosimii. Both the transitional forms 

 and the true Prosimii disappear with the 

 Eocene, and in America both sets have quite 

 died out, while in the Old World the true 

 prosimian type has been continued to the 

 present age. We must await the results of 

 further investigations before we can decide 

 the question of the true relations of the 

 transitional forms, and, in particular, we must 

 ascertain the structure of the limbs of these 

 forms in order to determine whether they 

 were analogous to those of the present 

 Prosimii or to those of the Ungulates. 



Combining the results of pala;ontologicaI, 

 geographical, and zoological investigation we 

 can only say that the variously formed order 

 of the Prosimii must have had also a varied 

 oHgin, probably from marsupials, to which 

 many features of their organization point, and 

 that certain forms belonging to the order are 

 among the oldest Tertiary mammals known. 

 It is, at any rate, in the highest degree re- 

 markable that types, which were so abun- 

 dantly represented in North America in early 

 Tertiary times, have quite died out there. 



If this high antiquity of the Prosimii, 

 reaching back almost to the oldest strata from 

 which we have obtained any placental mam- 

 mals, has been demonstrated by palaeonto- 

 logical discoveries, this fact affords at the 

 same time a proof, that the formation of 

 hands, that is, of opposable thumbs or great 

 toes, does not represent, as was formerly be- 

 lieved, a further development of the foot, 

 but must rather be regarded as a more or 

 less primitive structure. 



But lastly, we may conclude from these 

 facts that no very close affinity can be de- 

 monstrated to subsist between the Prosimii 

 and the Simise, and hence between them and 

 man. With the exception of the opposable 

 first digits, which are, indeed, as we have 

 seen, a widely distributed common feature, 

 the Prosimii have not a single anatomical 

 character in common with the apes and 

 monkeys. The dentition, the most constant 

 of all anatomical characters, associates them 

 with the Insectivora; to include them among 

 the ancestors of man is to defy all the 

 principles of scientific investigation. 



