= The solubility of CO2 also makes an empirical correction necessary for reabsorption of the gas while the volume is undergoing reduction from 50-S cc. to a cc. In our apparatus, where S 50 cc., a = 2 cc., the factor is approximately 1.020, the reabsorbed CO2 being 2 per cent of the total. For the less soluble gases reabsorption may be kept negligible. No correction for vapor tension is required, since it is practically the same at the reading of both m and n. For a given gas volume the value of the pressure change (m — n) is inversely proportional to that of a. a may accordingly be so chosen that for the gas volumes obtained the percentage error in measuring a cc. of gas will be of the same order of magnitude as that in measuring the accompanying (mn) mm. of pressure change. The total volume A of the pipette chamber is a matter of convenience, but it is desirable to have it so large that the greater part of the dissolved gases shall be extracted. For analysis of 1 cc. of blood convenient magnitudes are A = 50, a = 2, S = 2.5. At 20° 1 volume per cent of gas under these conditions gives a reading of m n = 3.9 mm., so that if m n can be determined within 0.4 mm. the error is 0.1 cc. of gas per 100 cc. of blood. ADAPTIVE RADIATION AND CLASSIFICATION OF THE PRO BOSCIDEA1 BY HENRY FAIRFIELD OSBORN AMERICAN MUSEUM OF NATURAL HISTORY, NEW YORK CITY Read before the Academy, April 26, 1921 In 1900 the author predicted that the source of the mammalian order of the Proboscidea would probably be discovered in Africa. In 1901 Beadnell and Andrews revealed, through the Geological Survey of Egypt, the rich fauna of the Fayûm, southwest of Cairo, in which were found the remains of three proboscidean genera, named by Andrews Maritherium, Palæomastodon, Phiomia, confirmed by subsequent exploration and research to be the oldest proboscideans thus far known. Animals similar to Maritherium and Phiomia have since been reported by Pilgrim in southern Asia. These animals are now found to belong respectively to three distinct lines of the Proboscidea, namely, the moeritheres, the true mastodonts, the long-jawed bunomastodonts, as indicated in black on the accompanying diagram. They point, however, to a long antecedent origin and radiation. This is part of the evidence for an ancient adaptive radiation process by which it now appears that the proboscideans, like other hoofed mammals, were broken up into several great primary stocks way back in Eocene times, namely: An amphibious stock, adapted to rivers and swamps, of limited migration. An elephant stock, adapted to grassy plains, savannas, and steppes, of wide migration. These primary stocks gave off from two to six branches each, so that the Proboscidea as a whole are not two branched (i.e., mastodonts and elephants), as formerly supposed, but many branched or polyphyletic. The forest and savanna browsers and the grazers of the plains and steppes were the long distance travelers and from an African or Asiatic center in Eocene times they reached in the Middle and Upper Miocene all the continents of the world except Australia, while the amphibious forms remained in Africa and southern Eurasia. Certain of these branches, like the true mastodons, are of very great geologic antiquity. Intelligent, independent, well defended, resourceful, adaptive, we find eleven very distinct branches of proboscideans persisting into Upper Pliocene times, five of the least hardy of which became extinct during the colder conditions of the Lower Pleistocene. The known lines of evolution are shaded on the accompanying diagram; the unknown are left in white. The adaptive radiation may be expressed in a formal classification as follows: Amphibious and swamp-living stock I. MOERITHERIOIDEA (Maritheres) 1. Mæritheriini, amphibious or swamp-living forms known in the Upper Oligocene of Africa. II. DINOTHERIOIDEA (Dinotheres) 2. Dinotheriini, large amphibious forms frequenting the rivers of southern Eurasia throughout the Miocene to the close of the Pliocene. Forest and savanna grazers III. MASTODONTOIDEA (Mastodonts and Bunomastodonts) 3. Mastodontinæ, springing from Palæomastodon of the Oligocene of North 4 4. Serridentinæ, first known in the Middle Miocene of France and Switzerland, spreading over into India and North America; lacking the trefoils. BUNOMASTODONTIDAE, the bunomastodonts, springing from forms similar to the Phiomia of North Africa and separating into four main divisions: 5. Notorostrinæ, a special branch entering the Andean region of South America and spreading over the South American continent, distinguished by the loss of the lower tusks and the abbreviation of the jaw. 6. Longirostrinæ, typical long-jawed bunomastodonts arising in North Africa (Phiomia), spreading all over southern Europe, Asia, and North America, and giving off: 7. Rhynchorostrinæ, beaked bunomastodonts, known only in the southern United States and northern Mexico, with powerful downturned upper and lower tusks. FIG. 1. Diagram showing the present theory as to the adaptive radiation of the Proboscidea. June, 1921. IV. 8. Brevirostrinæ, short-jawed bunomastodonts, which imitate both the true mastodonts and the elephants in the abbreviation of the lower jaw and the early loss of the inferior tusks. These animals wandered all over Europe, Asia, and western North America. ELEPHANTOIDEA (the Elephant stock) 9. Stegodontinæ, the original members of which were doubtless ancestral to all the higher elephants, persist as an independent branch into the Lower Pleistocene of eastern Asia. 10. Loxodontinæ, embracing the great African division of the elephants beginning with Loxodonta antiqua of the Upper Pliocene, which wandered all over southern Eurasia and radiated widely over Africa. 11. Mammontinæ, including (a) the Southern Mammoths (Elephas planifrons of India and E. Meridionalis of Europe), from which is derived E. imperator of North America, and (b) the Northern Mammoths, which probably include E. columbi and the widespread E. primigenius of the northern steppes; tetradactyl pes. 12. Elephantine, the true elephants (E. indicus of India), which do not appear until the Upper Pleistocene; pentadactyl pes. This twelve-fold branching of the proboscideans is similar to the adaptive radiation which the author has traced in the evolution of the horses, of the rhinoceroses, and of the titanotheres, carrying the fundamental lines of separation back to the Middle Miocene as the most recent date, and to the Middle or Lower Eocene as the most remote date. It will be observed from the diagram that the shaded areas represent those phyla of which remains have been discovered. The large unshaded area includes the entire Oligocene, Miocenes, and Lower and Middle Pliocene history of the Elephantidæ which is still unknown but which is likely to be revealed at any time by discoveries both in Africa and in central Asia. A very striking fact is that the geologically earliest known member of the Elephantoidea is the Elephas planifrons of the Upper Pliocene of India, the apparent ancestor of the mammoths. 1 The first paper in this series is entitled, "A Long-jawed Mastodon Skeleton from South Dakota and Phylogeny of the Proboscidea," Bull. Geol. Soc. Amer., March, 1918; the second paper, "Evolution, Phylogeny, and Classification of the Proboscidea," Amer. Mus. Novitates, No. 1, January 31, 1921 (Osborn, 1921. 514); the third paper, "First Appearance of the True Mastodon in America," Amer. Mus. Novitates, No. 10, June 15, 1921; the fourth paper appears in the Bulletin of the Geological Society of America, under the title, "Evolution, Phylogeny, and Classification of the Mastodontoidea;" the present is the fifth paper. The Iconographic Type Revision will form one of the Memoirs of the American Museum of Natural History. 2 Herluf Winge, 1906, p. 172. 3 Ibid. It is a question whether this subfamily is nearest the Mastodontidae, with which its members are generally placed by European palæontologists. A CASE OF REARRANGEMENT OF GENES IN DROSOPHILA1 BY A. H. STURTEVANT COLUMBIA UNIVERSITY, NEW YORK CITY Communicated by T. H. Morgan, May 28, 1921 Seven mutant genes of Drosophila simulans have been shown to be allelomorphic to previously known mutant genes of D. melanogaster.2 Five of these lie in the X-chromosome, and a study of their linkage relations was shown to indicate that the sequence of the five loci concerned is the same in both species, and that the percentages of crossing over in comparable regions, while not indentical, is still not very different. The other two allelomorphic mutant genes, scarlet and peach, lie about 3 units apart in the third chromosome of melanogaster; in simulans they lie in the same chromosome (which is thus identified as the third one), but they were found to be at least 45 units apart. 3 More recently two more mutant genes of simulans that lie in the third chromosome have been studied. One of these, dachs, lies to the left of scarlet; the other, deltoid, lies between scarlet and peach. The latter, since it makes possible the detection of a portion of the double crossovers, has resulted in a more accurate determination of the scarlet peach distance. The map based on the linkage relations of these four loci (not corrected for unobservable double crossing over) is shown in figure 1. Both of the new mutant types, dachs and deltoid, resemble previously known mutant types in D. melanogaster. Dachs in melanogaster lies in the second chromosome; it is accordingly not surprising that tests have shown it not to be allelomorphic to dachs simulans. Deltoid resembles delta melanogaster. Since both genes are dominant, the usual test of allelomorphism could not be applied; but each has also a recessive lethal effect, and crosses of delta melanogaster by deltoid simulans have shown that the hybrids that receive both mutant genes do not develop. It follows that the two genes are allelomorphic. The map of the melanogaster third chromosome, including the known ends and the three loci occupied by parallel mutations, is shown in figure 2.5 A comparison of figures 1 and 2 shows that the three identical loci are not in the same sequence in the two species. Mr. D. E. Lancefield has obtained evidence suggesting a similar rearrangement of genes in the X-chromosome of D. obscura. His results were obtained before those here reported, but are not yet published. Since D. obscura has not yet been crossed with any other species, the evidence for identity of loci is not conclusive in this case. The only analogous case so far reported appears to be that briefly described by Bridges under the name of "vermilion duplication." In |