was able to demonstrate that crossing over had taken place in one chromosome and not in the other, while in two cases he showed that two crossover chromosomes were present in the exceptional daughter. He explained these facts as due to non-disjunction occurring at the equational division, and believed that they involved crossing over at the "four strand stage” in the primary oocyte.

Of the two certain cases of "equational" non-disjunction in willistoni, one gave a result like that just mentioned. The exceptional fly in this case came from an XXV female (W 1955) which had stubby, orange, small-bristle in one X chromosome, and orange, rough, short in the other. This female was crossed to a two-bristle, short-3 male and produced the following offspring: 135 daughters and 119 sons of the regular classes, 2 two-bristle, short-3 sons (secondary exceptions of the ordinary "reductional" type), and 1 stubby, orange, small-bristle daughter-an “equational" exception. This last female produced secondary exceptions as expected, but she also carried a sex-linked lethal so that her only surviving sons were stubby, orange, small-bristle. Her exceptional daughters, being of the same constitution, also gave this same lethal ratio, but breeding tests from her regular daughters revealed her constitution. By such means it was proved that she had one non-crossover chromosome carrying stubby, orange, and small-bristle, and one crossover chromosome carrying stubby, orange, small-bristle, rough and short, and the new lethal. A non-disjunctional strain was established from this female known as line D (table 1).

The other equational exception Is not of special interest since both of her chromosomes were non-crossover chromosomes, as far as the region that could be followed was concerned. It is not certain whether her mother, a descendant of line B, carried a Y chromosome. She gave rise to line C (table 1).

Additional possible cases of equational exceptions have been found but they could not be positively identified as such.

To secure XXY chromosome groups for cytological study the daughter of exceptional females from line A (W 1894b) were used. Theoretically half of these daughters should be of the desired constitution. No attempt

was made to determine whether or not this 1:1 ration was actually realized, but XXY individuals were found without difficulty in the material put up for cytological study.

Discussion. The evidence is not yet sufficient to indicate the exact relationship between the chromosomes of the two species considered here, but it does indicate that either the chromosomal resemblances are merely superficial or that the sex determining element (gene? or genes?) has been transferred from one chromosome pair to another. A comparison of the sex-linked mutant characters in the two species ought to throw some light on this question. It has not done so up to the present, however, for although we have obtained 27 such characters in willistoni they show so little resemblance to any in melanogaster (either sex-linked or non sexlinked) that they give no clue to chromosomal relationships.

The observed frequency of secondary non-disjunction in willistoni (average 1.7%) was less than that found by Bridges in melanogaster (4.3%). There is no indication at present as to why this should be the case unless the size of the sex chromosomes be considered a factor.

The "m" chromosomes are often difficult to detect. They may be lacking entirely in willistoni.

2 D. willistoni Sturtevant (D. pallida Williston).

Dr. Bridges kindly informs us that he has subsequently verified this conclusion. 4 We are indebted to Dr. José Nonidez for making the drawings for figures 3-10. Line D may possibly be an exception but the small numbers make this doubtful. Bridges, C. B., Genetics, 1, 1916 (16-52, 107-163).

7 Metz, C. W., J. Exp. Zool., 21, 1916 (213–276).

AN APPARATUS FOR DETERMINATION OF THE GASES IN BLOOD AND OTHER SOLUTIONS

BY DONALD D. Van SLYKE

HOSPITAL OF The Rockefeller Institute, New York

Communicated July 5, 1921

The apparatus consists of a pipette with the upper stem closed by a stopcock, the lower connected with a glass tube. The latter descends 800 mm., then turns at a right angle to connect with a levelling bulb and a mercury manometer open at the upper end. The pipette is calibrated at two points to hold a and A cc., respectively, as shown in the figure.

For an analysis the pipette is filled with mercury. The solution to be analyzed, followed by the reagents to free the gases (e.g., acid for CO2 in carbonates) is admitted with slight negative pressure through the upper cock, displacing mercury in the pipette. A Toricellian vacuum is created by lowering the levelling bulb, and the meniscus of the mercury in the

pipette is allowed to fall to the mark indicating A cc., as shown in the figure. Cock c is closed, and the pipette is shaken for the time required to establish equilibrium of the gases between the solution and the free

acc.

ACC.

Scc, of
solution

on the manometer (ʼn mm.).

space above it. One to two minutes usually suffice. Mercury is then readmitted at cock c until the gas volume in the pipette is reduced to a cc. Cock c is closed and the height of the mercury column in the manometer is read (m mm.). The zero point is then determined after expelling the gases from the apparatus, or after absorbing one or more of them by introduction of small, measured volumes of gas-free absorbent solutions (KOH for CO2, pyrogallol for O2) through the upper cock under slight negative pressure. After the gas has been removed the pressure is lowered until the free space above the solution is again a cc., and the zero point for the determination is read

The volume, V, of gas reduced to 0°, 760 mm., contained in the solution analyzed is calculated as:

T

=

n/273 760 T

absolute temperature, S = volume of water solution in the apparatus, a = solubility coefficient of the gas in the solution (the cc. of gas, reduced to 0°, 760 mm., dissolved by 1 cc. of solution in equilibrium with the gas at 760 mm. tension).

Sa The term which corrects for the portion of gas remaining in A S' solution when equilibrium is reached, may be negligible for the less soluble gases, such as oxygen and nitrogen, but not for CO2. The term is derived as follows. If Vs volume of gas (measured at 0°, 760 mm.) held in solution by the S cc. of solution, and p

=

=

partial pressure of the gas

In case x cc. of absorbent solutions are introduced, a correction to n is necessary. It is ascertained by determining m for S and for S+xcc. of water, respectively, the dissolved gases being removed by expulsion.

=

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 (m − n) 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.
A mastodont stock, adapted to forests and savannas, of wide 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. Moritheriini,2 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)
MASTODONTIDAE OR "true mastodonts," including the subfamily

3. Mastodontinæ, springing from Palæomastodon of the Oligocene of North
Africa, and terminating with Mastodon americanus

of the Pleistocene forests of North America; grinders lophodont, lacking trefoils.

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.