3^8 



NA TURE 



{March i6, 1876 



teeth. These are forms for fuller information upon which 

 we anxiously wait. 



The negative evidence (which of course must be re- 

 ceived with the greatest caution in palaeontology) of the 

 absence of remains of any of these animals in the true 

 Miocene or Pliocene deposits of North America, indi- 

 cates that the race became extinct at least in that land, 

 though it possibly may have emigrated elsewhere, and 

 perhaps in Asia, may have laid the foundation of that 

 family which first appears in the Old World under the 

 more familiar aspect of typical Proboscideans. While, 

 however, there are no grounds for assuming that the 

 latter were derived directly from the Eocene Bathmodons 

 and Uintatheriums, it is not too much to look upon these 

 as affording some indications of the steps by which the 

 process might have taken place, and, as such, their dis- 

 covery is one of the most interesting that has been re- 

 vealed by modern palaeontological research. 



It should be mentioned that Marsh, who has given us 

 very full information upon the osteology and dentition 

 of this group, has made of Uiiitatherhan and its imme- 

 diate allies a peculiar order of mammals, to which he 

 gives the name of Dinocefata, while Cope, who formerly 

 included them in the Proboscidea, and placed Bathmodon 

 and its alhes in the Perissodactyla, has recently formed an 

 order called Atnblypoda, containing two sub-orders, of 

 which Dinocerata is one, and Pantodonta {Bathtnodon 

 and Metalophodon) the other. 



The tertiaries of South America have yielded some 

 very remarkable forms of mammalian life, the nature and 

 affinities of which have greatly puzzled all zoologists who 

 have attempted to unravel them. Macrauchetiia has 

 been already described among the Perissodactyle Ungu- 

 lates, of which group it is undoubtedly a member, although 

 in some characters somewhat aberrant. The articulation 

 of the fibula with the calcaneum is an Artiodactyle, or 

 perhaps generalised character. The teeth ally it to 

 Palseotherium and Rhinoceros. Homalodontotherimn 

 from the banks of the River Gallegos, South-east Pata- 

 gonia, is known by the teeth alone, which, though very 

 generalised, are on the whole rhinocerotic. Nesodon, 

 from the same locality, also only known by the denti- 

 tion and some parts of the skull, connects the last and 

 Macrauchenia with Toxodon. These three genera have 



the typical dental formula of i^c-p~ni^=±\. 



.3143 

 Toxodon is an animal about the size of a hippopotamus, 

 of which many specimens have now been found in Pleis- 

 tocene deposits near Buenos Ayres, which have been 

 described by Owen, Gervais, and Burmeister. The teeth 

 consist of incisors, very small lower canines, and strongly 

 curved molars, all with persistent roots ; the formula 



being apparently i Z c ~ p ~ in - = 38. The cranial cha- 



3133 

 racters exhibited a combination of those found in both 

 Perissodactyles and Artiodactyles, but the form of the 

 hinder part of the palate, the absence of an alisphenoid 

 canal, and especially the tympanic being firmly fixed in 

 between the squamosal and the exoccipital, ankylosed to 

 both, and forming the floor of a long, upward directed 

 meatus auditorius, is so exactly like that of the Snina, 

 that it is difficult to believe that it does not indicate some 

 real affinity to that group. These characters seem 

 to outweigh in importance those by which some zoolo- 

 gists have linked it to the Perissodactyla, and the absence 

 of the third trochanter, and the articulation of the fibula 

 with the calcaneum tell in the same direction. The struc- 

 ture of the feet is not. known, but it is probable that it 

 had five toes on each. 



Mesothertum, Serres, also called Typotherhiin by Bra- 

 vard and Gervai<, was an animal rather larger than a 

 Capybara, and of much the same general appearance. 

 Its skeleton is completely known, and shows a singular 

 combination of characters, resembling Toxodon, or a 



generalised Ungulate on the one hand, and the Rodents, 

 especially the Leporidce on the other. In the presence of 

 clavicles, of five toes on the fore-foot and four on the 

 hinder, it differs from all existing Ungulates, and yet if 

 it is considered as a Rodent, it must be looked upon 



as a most aberrant form. The teeth are / 1 ^ - -j ?. 



2 o -^ I 



in - = 24. Although our knowledge of many of these 



forms is still very limited, we may trace among them a 

 curious chain of affinities, which, if correctly interpreted, 

 would seem to unite the Ungulates on the one hand, with 

 the Rodents on the other ; but further materials are 

 needed before we can establish with certainty so impor- 

 tant a relationship, one which, if true, would alter mate- 

 rially some of the prevailing views upon the classification 

 of mammals. It may be convenient provisionally to in- 

 clude those Ungulates which are neither Artiodactyla 

 nor Perissodactyla, under a third heading, of which Poly- 

 dactyla ^ would be the appropriate designation ; though 

 there is no evidence that they form such a homogeneous 

 group as either of the other two. 



( To be continued. ) 



PROF. HUXLEY'S LECTURES ON THE EVI- 

 DENCE AS TO THE ORIGIN OF EXISTING 

 VERTEBRATE ANIMALS'^ 

 I. 



TTWENTY years ago the arguments as to the causes of 

 ^ the phenomena of organic nature, brought forward 

 in support of the then recently advanced views of Mr. 

 Darwin, were largely speculative ; all one could hope to 

 show was that no valid objections could be urged against 

 the theory of evolution. But since that time " many have 

 run to and fro and knowledge has been increased " ; the 

 question has come out of the region of speculation into 

 that of proof ; every day increases our familiarity with the 

 phenomena of life on the globe in antecedent ages, and so 

 gives us the only valid evidence obtainable as to the 

 evolution of living things. 



When we consider any animal at the present day there 

 are three hypotheses which may be put forward with 

 regard to its origin : that it arose out of nothing, that it 

 had its origin from dead inorganic matter, or that it arose 

 as a modification of some pre-existing living being. It is 

 hardly worth while to consider the two first of these 

 hypotheses — for the first it would be utterly impossible to 

 obtain any evidence, and the second is devoid ot all ground 

 of analogy, and opposed to all our knowledge of what 

 actually takes place. The last, on the other hand, should, 

 if true, be capable of some sort of proof — at any rate it 

 can be brought to the test of facts. 



It is quite conceivable that all evidence as to the origin 

 of an animal may have disappeared, and that the problem 

 becomes, in consequence, insoluble by direct evidence, 

 analogy and probability being the only guides left. As a 

 matter of fact, however, we possess in the 70,000 feet of 

 stone, gravel, sand, &c., which form the earth's crust, 

 fossil remains imbedded in 'chronological order, and in 

 many cases so perfectly preserved, that all important 

 details can be made out almost as well as in the recent 

 state. 



The plan adopted in these lectures will be not to give 

 all obtainable evidence with regard to the origin of each 

 group of vertebrate animals, but to select from each class 

 one or two definite cases of living animals, and to see 

 what evidences can be obtained, by going back in time, 

 as to the way in which they have come about, or at any 

 rate as to the extent of the duration of their existence. 



1 An extension of the order Toxodontia of Owen, and Ungiilata wulti- 

 digitafa of Burmeister. 



2 A course of six lectures to working men, delivered in the theatre of the 

 Royal School of Mines. Lecture I., Feb. 28. 



