June, 1903/ 



KNOWLEDGE, 



12f 



Every day we have proofs to the contrary. If we examine 

 into the conditions of life, it would not be difficult to con- 

 clude that terrestrial chemistry does not necessarily include 

 the universal vital circle. To limit the work of Nature to 

 the sphere of our knowledge is to reason with singular 

 childishness. Of old, our fathers ('oniudered the four 

 elements " earth, air, fire, water " as the principles of all, 

 and saw in them the conditions of life. How many solemn 

 dissertations have been written on this subject? To-day 

 we affirm the necessity of carbon for the constitution of 

 living organisms. But no one knows what carbon is. 

 Our successors will, no doubt, smile at our assertions, and, 

 doubtless, the iuhaliitants of the systems of Eigel, and of 

 Denel) — stars characterised l)y the rays of titanium and 

 silicon — would understand nothing of the necessity for 

 carbon. 



The careful study of our planet shows tliat the forces of 

 Nature have Life as their supreme end. 



Yes, life is universal, and eternal, for time is one of its 

 factors. Yesterday the moon, to-day the earth, to-morrow 

 Jupiter. In space there are both cradles and tombs. The 

 red carbon stars will soon be dead ; the hydrogen stars 

 like Vega and Sirius are the stars of the future ; Procyon, 

 Capella, Arcturus, are the stars of the present. Aldebaran 

 seems to be already an autumn f i-uit Let us open the eyes 

 of our understanding, and let us look beyond ourselves 

 in the infinite expanse at life and intelligence in all its 

 degrees in endless evolution. 



THE PAL^EONTOLOGICAL CASE FOR 

 EVOLUTION. 



By R. Lydekker. 



(Continued from patje 102.J 

 Dismissing thus briefly a very interesting portion of our 

 subject, we proceed to bring to the reader's notice some of 

 the most important lines of mammalian descent which 

 have been worked out on palaeontological evidence. The 

 most famous and most ividely known of these is the horse 

 series, which has been so frequently described in full 

 detail that a very short notice will suffice here. Starting 

 with the little hyracothere of the TiOndon Clay — a short- 

 limbed and short-necked ungulate of the approximate size 

 of a fox, with short-crowned cheek-teeth, the socket of the 

 eye completely open, the lx)nes of the lower jiart of the leg 

 (radius and uhia in front, and tibia and fibula behind) 

 separate, and four front and three hind toes — an almost 

 complete passage can be traced through the extinct three- 

 toed horse-like ungulates of the middle and upper portions 

 of the Tertiary period to the single-toed horses, asses, and 

 zebras of the present day. The moditit-ations include a 

 great increase in bodily si/.(>, the lengthening of the crowns 

 of the cheek-teeth coupled with a marked increase in the 

 complexity of their structure, tiie cuch)sure of the socket 

 of the eve by a bony ring, the degeneration of the ulna 

 and fibula and the fusion of their upjier porticms with the 

 radius and tibia respectively, the early loss of the fourth 

 front toe, and the gradual reduction in the size and length 

 of the lateral toes of the tri<lactyle members of the series, 

 till tliev are represented in the modern horses only by the 

 so-(n!le<l splint-bones attached to the sides of the upper 

 hall' nf the cannon-bone of the greatly enlarged middle 

 digit. The five-toed ancestor of the little hyracothere 

 is not yet definitely known, but it was proliably 

 not far reniovod from the pheiiacodus of the lower 

 Eocene. The similarity between the form of the skull of 

 the little hyracothere and that of the luoch'rn horse is most 

 reiiiiirkable, and is well shown in a series of models recently 

 addiMl to the cidlection in the Natural History Museum. 



So far as human eye can see. the horse has iiractically 

 reached the supreme stage of evolution, so far as its 

 skeleton is couceined, of which its organisation is capalde ; 

 the only improvement that suggests itself being the total 

 abolition of the useless splint-bones, which are apt to Ije a 

 cause of disease. Not the least curious feature in this 

 remarkable series is its repetition in the North American 

 strata ; a repetition which has given rise to the suggestion 

 that the modern horses have had a dual origin, one branch 

 developing in the Old World and a second in the New. 

 On the whole, however, it seems more probable that the 

 line of development, which took place when the Eastern 

 and Western hemispheres were much more closely con- 

 nected by way of Beiing Strait than at present, was single. 

 It may "be added that the ancestral horses, such as the 

 hyracothere, were closely allied to the lophiodons and 

 palajotheres of the Tertiaiy, which in their turn lead on 

 towards the tapirs and rhinoceros, so that all the earlier 

 odd-toed ungulates were more or less nearly related. 



A most remarkable instance of a line of development 

 parallel to that of the horse series is presented by certain 

 South American Tertiary ungulates telonging to an extinct 

 subordinal group allie<l to the perissodactyles or existing 

 odd-toed foi-ms. In the most generalised representative 

 (Theosodun.) of the group in question the feet were three- 

 toed, with the lateral digits functional and of about the 

 same relative size as in the modern tapirs. In the next 

 form, Pfoienifheruim, the lateral toes have become much 

 smaller and shorter in proportion to the large central one, 

 and no longer touched the ground in walking. Finally, in 

 Thoatherium, according to the Argentine palaeontologists, 

 only the single median digit remains in each foot ; even 

 the" splint-bones having disappeared in the hind-limb, 

 although minute vestiges of their upper extremities persist 

 in the fore-foot. If the restoration be correct, Thoatherium 

 was thei-ef ore an even more specialised animal in regard to 

 foot-structure than the modem horses. The two lines of 

 evolution presented respectively by the horses and the 

 proterotheres form, perhaps, the most remarkable instance 

 of parallel development with which we are yet acquainted. 

 A somewhat curious, and at present inexplicable, difEerenc<; 

 in regard to the development of the terminal joints of the 

 toes is, however, noticeable in the two series. In the 

 earlier members of the horse series this segment is com- 

 paratively narrow and displays a median cleft, but in the 

 later forins the bone widens and the cleft disappears. 

 Precisely the reverse of this occurs in the proterothere 

 series, the terminal bone of each digit teing broad and 

 entire in the earliest form, and narrow and cleft in the 

 latest. 



The proterotheres are, however, by no means the only 

 extinct South American ungulates d'isplaying evidence of 

 progressive development. In some of the latest Tertiary 

 deposits of the country— in-obably belonging to the 

 human period— Darwin discovered certain more or less 

 fragmentary remains of an ungulate with the general 

 proportions" and size of the modern camels. Subsequent 

 discoveries showed that the macniuchenia, as it is called, 

 presents the unique pecidiarity that the nasal chamber 

 opens in the centre of the forehead, instead of at the 

 extremity of skull. Allied but mucli smaller animals 

 from the earlier Tertiary strata of Patagonia exhibit a 

 gradual transition from the macrauchenia in regard to the 

 position of tlu' external aperture of the nose-cavity towards 

 the normal mammalian type. And since they likewise show 

 a transition in respect of dental characters, which are very 

 aberrant in macrauchenia, that extraordiijary creature is 

 brought into line with less aberrant members of the 

 unguhite order. 



In the tapirs ami rhinoceroses syiecialisation has not 



