December 28, 191 ij 



NATURE 



293 



series of pyrheliometric determinations at Washington (sca- 

 ievel), Mt. Wilson (1800 metres), and Mt. Whitney (4420 

 metres), Mr. Abbot concludes that the most trustworthy 

 value of the " solar constant " is 1-95 calories per sq. cm. 

 per minute. 



An important resolution was adopted providing that in 

 future position angles round the sun's limb should be 

 measured from the north to the east. This is opposite to 

 the procedure followed during the last forty years in Italy, 

 but Prof. Ricco thought that the Soc. degli Spettroscopisti 

 Italiani would now be willing to agree to the change, in 

 order that all observers should have the advantage of a 

 uniform system. 



In the reports on sunspot spectra the concurrent result is 

 that the various metallic lines are, on the whole, affected 

 in a systematic manner, such that the arc-f^ame lines are 

 strengthened, normal arc lines unaffected, and enhanced 

 (spark) lines weakened in spots. Certain elements — 

 vanadium, titanium, scandium, &c. — show greater tendency 

 to strengthening than others. With regard to the question 

 (jf variation, it is evident that at least during the period 

 of five years about the last maximum, no decided changes 

 have been evident in the general spot spectrum. With 

 instruments of very large dispersion certain changes have 

 been noticed which, as before mentioned, are attributed to 

 variations of intensity in the magnetic field of the spot 

 vortex. Six observers have agreed to subdivide the region 

 B — F for the continuance of visual observations of special 

 phenomena. 



The third session, presided over by Prof. E. B. Frost, 

 was occupied with reports on the observations of solar 

 rotation, work with the spectroheliograph, and an address 

 hy M. H. Dcslandres on the " Motions and Forms of Solar 

 \'apours." 



The concluding sitting was mainly occupied with ques- 

 tions of administration, the chief point of interest being the 

 enthusiastic adoption of a motion to extend the scope of the 

 union to include astrophysics. A committee was appointed 

 examine and report on the question of classification of 



liar spectra. 



It was announced that in all probability a solar observa- 

 tory would be established in Japan in the near future. 



the next meeting of the Solar Union will be held in Bonn 

 '" 1013- Charles P. Butler. 



A 



IBk ORIGIN OF MAMMALS. 



N outstanding feature of the zoological section at the 

 Portsmouth meeting of the British Association was 

 an excellent discussion on the above subject, in opening 

 which Prof. G. t^lliot Smith laid special stress on the 

 influence exerted by the evolution of the brain in making 

 mammals what they are and in supplying evidence show- 

 ing whence they came. He pointed out that while all 

 living marsupials are specialised in greater or less degree, 

 so that no one of them can be looked upon as ancestral to 

 the Eutheria, it must be admitted that the more highly 

 specialised Eutheria must have passed, in the course of 

 their phylogeny, through a stage not very different from 

 that represented by Perameles, and that therefore there 

 was a metatherian stage in the ancestry of the Eutheria. 

 The mode of development of the blastocyst and the presence 

 ^f a shell membrane, the arrangement of the hippocampal 

 formation and cerebral commissure, and many other struc- 

 iural features, indicate that in most respects the marsupials 

 lave retained, in far greater measure than the Eutheria, 

 lie features distinctive of their common ancestor. Turn- 

 ng to the monotremes, not only is the skin and its hairy 

 md glandular epithelium typically mammalian, but also 

 he alimentary canal and liver, the diaphragm, the audi- 

 lory ossicles and their mode of development, and the organ 

 >f Jacobson ; in the brain the complex specialisation of 

 lie hippocampal formation and its curious fascia dentata 

 —so peculiarly distinctive of Mammalia — is carried to a 

 legree of differentiation at least as great as in other 

 nammals ; the characteristically mammalian neopallium 

 « present, and emits a system' of projection fibres form- 

 ng pyramidal and cerebro-pontine connections, as in other 

 mammals. 



Thesp and other facts demonstrate the kinship of mono- 

 remes to other mammals, and establish the monophyletic 



NO. 2200, VOL, 88] 



derivation of the Mammalia. But living monotremes are 

 separated by a wide interval from Meta- and Eutheria. .At 

 a very early stage in the history of Mammalia, soon after 

 the acquisition of skin, hair, milk glands, and the appear- 

 ance of the typical hippocampus and neopallium, the 

 Prototheria divided into two phyla, one of which retained 

 the generalised features and the other specialised. From 

 the former the common metatherian ancestors of all the 

 Metatheria and Eutheria sprang by gradual transforma- 

 tion ; from the latter were derived the living monotremes, 

 which display a high degree of specialisation in associa- 

 tion with the fixation of certain very primitive phases of 

 mammalian structure, showing what the primitive 

 mammal, just emerged from the reptilian stage, was like. 

 All mammals have sprung from an oviparous prototherian 

 stock, which, though vastly different from living mono- 

 tremes, still deserved the name Prototheria ; and there is 

 an overwhelming mass of evidence — anatomical, embryo- 

 logical, and palteontological — to prove that the mammalian 

 phylum sprang from the Reptilia, although certain features 

 — the occipital condyles, the mesenteric vessels, the epi- 

 glottis, the mode of development of the heart, the nature 

 of the skin and its sense organs, the auditory ossicles, and 

 the early phases of the eutherian blastocyst — have been 

 cited as arguments for an amphibian, in opposition to a 

 reptilian, ancestry for mammals. But Hill has demon- 

 strated the thoroughly sauropsidan derivation of the mam- 

 malian mode of blastocyst formation, while Osborn, 

 Broom, and others have shown that the bicondylar 

 arrangement of the amphibian occipital bone has persisted 

 in many extinct reptiles, and especially in the Theriodonts, 

 which present such a remarkable series of mammalian 

 resemblances in their skeletons. 



The process of differentiation of the mammalian hippo- 

 campal formation becomes intelligible only when the pre- 

 paratory phases, represented in the reptilian brain, are 

 known. In the amphibian brain, on the contrary, the 

 cortical formation has become so specialised, or perhaps 

 so degenerate, in comparison with that of its forerunner — 

 the Dipnoi — or its successor — the Reptilia — that it must 

 be regarded as being off the path which led to the 

 Mammalia. In spite of the certainty that the mammalian 

 brain passed through a reptilian stage in its phylogeny, 

 the brain of no living reptile fulfils the conditions required 

 in the actual ancestor of the Pro-mammalia. The brain 

 of Sphenodon represents a blending of primitive features 

 with lacertilian and chelonian characters, but it inclines 

 too decidedly to the Lacertilia to afford a type of the 

 ancestral reptilian brain. The extinct Therapsida (in- 

 cluding Cynodontia) present a blend of primitive reptilian 

 and primitive mammalian features, many of the characters 

 of the skull of Rhynchocephalia, of the polyprotodont 

 marsupials, and of the Insectivora being reproduced with 

 surprising exactitude, as Watson has recently shown, and 

 in the limbs prototherian peculiarities are often closely 

 foreshadowed. If the actual ancestor be not discovered, 

 the group of Cynodontia provides so many forms present- 

 ing mammalian characters of skull and teeth, limbs and 

 trunk, that it is no longer possible to refuse to recognise 

 these extinct forms as the representatives of the order to 

 which the ancestor of the Prototheria belonged. Prof. 

 Elliot Smith held that the ancestor of the Mammalia was 

 scaly and laid eggs provided with a large amount of 

 yolk, to mention only two obvious points among the 

 definitely reptilian characteristics of the Pro-mammalia, 

 and repeated that there is an extinct group of reptiles — 

 the Cvnodontia — which includes representatives conforming 

 in almost every detail of structure to what would be e.K- 

 pected in the near relatives of the earliest mammals, 

 whereas there is no group of .Amphibia which fulfils these 

 conditions. 



It seems im()ossibIe to derive either reptiles or mammals 

 from the true .Amphibia. In the course of evolution from 

 the dipnoan stage the amphibian brain has in great 

 measure lost precisely those features which were essential 

 if it had to develop into the reptilian or mammalian con- 

 dition. The features of the brain in Dipnoi so definitely 

 foreshadow the conditions seen in the Reptilia that it is 

 difficult to belie^'e the Dipnoi can be far removed from the 

 direct path leading to the Amniota ; but the dipnoan brain, 

 in its general plan, though not in the histological detail of 



