294 



NATURE 



[December 28, 191 1 



its cortex, b eMmtially amphibian. This fact, talcen in 

 conjunction with the palaeontoloffical evidence, suggetU 

 that the stcguccphalian brain may o»,s^ bridged ttte interval 

 between thuee o( Dipnoi and Reptilia. Pcrhape both 

 Amphibia and Reptilia have been derived from Stego- 

 cephalia. Recent reaearch, especiatly on foistls from tiie 

 P«-mian of Texas, has brought to light stegocephalians 

 •u cioeely resembling reptiles, and reptilian remains so 

 stcgocepbalian, that there can no longer be any questioo 

 as to tne genetic relationship of the two groups. 



Prof. EUiot Smith remarked that it is unfortunate that 

 nothing is known of the brain in the Cynodontia, for he 

 thought that the transformation of its cortex v'-' •■ -ve 



Slay«l a leading part in the evolution of tiie '. 



room states that the South African Therln^ w 



which mammals were derived became distingui&ltcU Irum 

 their American allies by the development of powerful limbs, 

 ai\d that " it was the lengthened limb that gave the start 

 to the mammals." •*' When the Therapsidan took to walk- 

 ing with its feet underneath and its body off the ground 

 it first became possible for it to become a warm-blooded 

 animal. Alt the characters that distinguish a mammal 

 from a reptile are the result of increased activity — the soft 

 flexible skin with hair, the more freely movable jaws, the 



g;rfect four-chambered heart, and the warm blood." But 

 room confesses his inability to e.xplain how this fateful 

 lengthening of the limbs was caused. Prof. Elliot Smith 

 suggested that a realisation of the changes which took 

 place in the brain in the transition from reptiles to 

 mammals would seem to indicate an explanation of this 

 end the acquisition of many other mammalian features. 



The development of a definite neopallium (the cerebral 

 cortex sensu stricto), the lengthening of the limbs, the 

 increased activity, the freeing of the skin of its mail-like 

 coat of scales and conversion of it into a highly developed 

 tactile organ — all these events occurred at about the same 

 time, and had a reciprocal influence one upon the other. 



By the time the Reptilia were evolved the cerebral 

 hemisphere had reached a stage of development which 

 opened up vast possibilities of new developments. Though 

 the cerebral cortex was still mainly olfactory in function, 

 tactile, gustatory, visual, and perhaps auditory impulses 

 ^•ere able to make their entry into it ; but it exercised 

 little direct control over the movements of the body, which 

 ■were still regulated by the midbrain. The possession of 

 this potential receptive organ in the cortex for receiving 

 tactile impressions and bringing them into relation with 

 impressions from the other sense organs gave an added 

 importance to tne tactile sensibility of the ridges of skin 

 that intervened between the scales of the Hypotherian. 

 Moreover, more precise movements of the limbs became 

 possible, because more exact information was being pro- 

 vided of the positions of the limbs by these tactile 

 impressions. 



The enhanced importance of the skin as a tactile organ 

 led to the atrophy of the scales, perhaps by a process of 

 natural selection ; and the greater perfection of the 

 tactile sensibility of the skin, and of its receiving 

 and recording apparatus in the cortex, reacted mutu- 

 ally one upon the other and gave birth to the neo- 

 pallium. It is not without significance that from its 

 earliest appearance the neopallium performed the function 

 of regulating " skilled " movements of the whole body, 

 i.e. such actions as are possible only when there is a 

 highly developed tactile information bureau to render nicely 

 adjusted movements possible. Moreover, quickness and 

 increased activity are made possible by the neopallium, 

 because it was put into direct connection ab inilio with all 

 the motor nuclei in the whole central nervous svstem bv 

 the pyramidal tract (which developed pari passu with the 

 evolution of the neopallium), and also with the cerebellum 

 (by the simultaneous development of the pons), which 

 enabled the creature to coordinate the muscular activities 

 of its whole body to perform quick, accurately adjusted, 

 and skilled movements. It is such developments as these 

 that made the mammals what we know them to be. that 

 give them their dominant position and their plasticity, or 

 power of rapid adjustment to varying environment. 



It is only when such skilled movements are possible that 

 long limbs, capable of supporting the body, can become 

 useful appendages. The fact that such limbs were making 

 NO. 2200, VOL. 88] 



dieir appearance in the TherapskU in Triaaslc timei> 

 tangible evidence of the birth of the neopallium in ti. 

 pro-mammals. 



Prof. Arthur Keith, in maintaining that mamm.-i!- -■ 

 not from reptiles, but from Amphibia, remarked ' 

 divergence between his views and those of Pre! 

 Smith was not really so great, as the qucktion 

 not the Amphibia and reptiles of the present, but 

 forms in regard to some of which it was difficult 

 to which of these phyla they should be referred 

 common stock from which reptiles, birds, and maun: 

 had been derived possessed three characters: — (i) an • 



f;iving rise during development to an amnion and alLmt< 

 2) the beginning of a cerebral cortex; and (3) lungs fii 

 and emptied by movements of the body wall. ProT. K- 

 regarded this common ancestor as more amphibian ti 

 otherwise. He devoted special attention to tlie tl. 

 character above named, and pointed out there was not 

 any living reptile a trace of a diaphragm, and that ' 

 lungs of reptiles were essentially different in «•-••'• 

 from those of niammals, and, further, the movei: 

 the body wall were different in the two phyla. He : 

 that the evolution of a new type of respiration, in wh. 

 the whole body wall became a means of expanding ; 

 body and filling the lungs, was a great 

 and he considered that this occurred in a: 

 not far removed from the Dipnoi, and coiumwu ui.u i, 

 was a common type (amphibian) from which the th: 

 types of respiration — reptilian, avian, mammalian — 1 

 been evolved. He also referred to the presence of H' 

 bundle, which is found only in the heart of mammals, :■■ 

 suggested that this arose in the EHpnoi, and was tra 

 mittcd through an ancient amphibian. Prof. Keith thou, 

 that an early amphibian, arising near the beginning of ir 

 Permian, was the stock from which came the higher vert - 

 brates. 



Dr. C. W. Andrews remarked that the agreement 

 the skeleton of Cynodonts with that of mammals is 

 remarkable that it is impossible to believe it arcidcn' 

 Possibly in Middle Permian times lived some small anii; 

 of this group from which the mammals arose. '1 

 shoulder girdle, atlas, and lower jaw of some Theriodc: 

 represented transitions from reptilian to mammalian cor 

 tions. The dentary became greatly enlarged, owing to ■ 

 differentiation of the teeth, especially grinding teeth, 

 tended backwards, and acquired articulation with 

 squamosal, leaving the quadrate and articulare on 

 inner side. Some of the South African Therapsida y 

 sent so close an approach to mammalian characters tha; 

 seems impossible to believe that the Mammalia can ha 

 arisen from any other group. 



Dr. Marett Tims pointed out that if the dentiti. 

 of the monotremes and of the Metatheria and Euth- : 

 be considered, the monophyletic derivation of 

 mammals does not appear to be full)' esta 

 In the marsupials and Eutheria generally 

 the Rodentia out of account for the moment! 

 dentition is of the type which may be referred to 

 trituberculate, though not of the ti-ituberculate pattr: 

 while the dentition of the monotremes is of an enti: 

 different nature, being referable to that of the fossil Mu 

 tuberculata. Dr. Tims said that his investigations on : 

 tooth germs of the Caviidae lend support to the view th 

 as already urged by Dr. Forsyth Major, the dentition 

 these rodents has a multituberculate character. On th 

 and other grounds Dr. Tims was disposed to suggest lii- 

 possibility of the diphyletic origin of mammals, and to 

 believe that monotremes, and possibly rodents (though with 

 much greater doubt), may have sprung from a different 

 stock than that from which the marsupials and remaining 

 Eutheria have arisen. J. H. A. 



VERTICAL CURRENTS IN THE ATMOSPHERE. 

 TN a paper entitled " Die Messung vertikalen Luftstrdm- 

 unffen," Dr. Paul Ludewig-, of the University of 

 Konigsberg, describes some experiments made in three 

 balloon ascents, for the purpose of determining the vertical 

 currents in the atmosphere. The lack of information on 

 this important point is made painfully evident at intervals 

 in the inquiries into aeronautical disasters. The problem is 



