Page images
PDF
EPUB

In the meantime Mr. Baly has made exact measurements of the lines of the neon spectrum, at the same time eliminating all the lines which belong to argon and to helium by superposed plates. The values were compared with iron lines photographed upon the same plate, and the measurements were carried out by means of different pairs of these known lines. The most important lines are the following:

MOST IMPORTANT LINES OF THE NEW SPECTRUM.

[blocks in formation]

Blue

4722
4710
4709
4704

Up to the present we have had little time to study thoroughly the other companion of argon in the atmosphere. Dr. Travers and I have, however, worked upon it. The heavier fraction of the air contains three

one in yellow and one in green, we are in much the same position. We have collected a considerable quantity of the impure gas, which shows the spectrum finely, although that of argon is also present. We hope that we shall soon be able to pursue this portion of our work further. We can merely note here that the specific gravity of the gas which shows this spectrum in such a marked way is not far different from that of argon.

The heaviest of these gases we have 4716* weighed, although in impure condition. Its density is 32.5. I need not call your attention to the fact that there is space for an element of the helium group between bromin and rubidium. Such an element should have an atomic weight of 81-83, which corresponds to a density of 40.5-41.5, under the very probable supposition that, like the other gases of this group, it is monatomic. The spectrum of this gas, which we have named 'xenon '-the stranger-has many lines; none of these are of marked intensity, and in this respect the spectrum resembles somewhat that of argon. It is also analogous to argon in another particular, that the spectrum undergoes a remarkable change when a Leyden jar is put into the circuit. As with argon, many new, blue and green lines appear, while other lines, mostly in the red, either disappear or lose much of their intensity. Further than this we have not proceeded in studying xenon; for our attention has been given chiefly to neon, as well as to a problem regarding argon.

gases, one of which appears very perplexing. We have named it 'metargon.' This gas remains, mixed with excess of argon, after the evaporation of liquid air or argon. Up to this time we have not succeeded in obtaining it in a condition free from argon. Its peculiarity is that when it is mixed with oxygen and subjected to the influence of the electric spark in presence of caustic potash it shows constantly the 'Swan-spectrum' as of carbon monoxid. We have treated a mixture of carbon monoxid and argon in a similar way, and, after fifteen minutes' sparking, all the carbon had disappeared; in a Plücker tube no trace of the carbon spectrum could be recognized. I will, however, not yet venture to express an opinion as to the nature of this gas. It needs further investigation, and for this at present we have no time.

As regards krypton, which is distinguished by three brilliant lines, one in red,

* The third figure in this number is probably a misprint (Tr.).

We have repeatedly met the question: "Are the properties of argon not appreciably changed by the presence of this new gas?" In order to settle this question we have fractioned 25 cubic centimeters of liquid. argon several times and have collected separately about 200 cubic centimeters of the lightest and as much of the heaviest fraction. This operation was repeated three

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][ocr errors][merged small][merged small]

Since

The first fraction possesses, as appears from the table, a lower density and also a lower refractivity. The other fractions vary very little from each other. these determinations were made by using only 30 cubic centimeters, we have weighed 160 cubic centimeters of the fifth and sixth

fractions. The first determined density of the fifth fraction was 19.935, but at a pressure of 5 millimeters the spectrum of nitrogen was easily recognizable in a Plücker tube. After the gas had been again purified by sparking, until all the nitrogen had been removed, the density was 19.957. In two experiments the fourth fraction of gas gave 19.952 and 19.961. We must then accept the true density of argon as not far from 19.96. Independently Lord Rayleigh and I found the density of argon to be 19.94; so it is clear that the impurities of neon and the heavier gases have little influence. The somewhat greater density of pure argon arises from the fact that the neon, which is the chief impurity present, has been removed; the influence of the other gases cannot be recognized, owing to the insignificant quantities present. In fact, in 15 liters of argon we found no appreciable trace of xenon; it can

* Contained nitrogen.

be prepared only out of large quantities of liquid air.

I must take this opportunity of thanking you most sincerely for the honor you have done me in inviting me to deliver this address. It has been said by some scientist that the greatest joy of life lies in discovering something which is new. There is, however, another joy almost equally great, that of making known the results of an investigation to one's fellow scientists. This joy, my friends, you have given me to an extreme degree, and for this I express to you my warmest thanks.

A CASE OF CONVERGENCE.*

IN 1859 Girard (Proc. Acad. Nat. Sc. Phila., p. 62) described a small blind fish, Typhlichthys subterraneus, from Bowling Green, Ky. This species has since been found to be abundant in the subterranean waters east of the Mississippi and south of

the Ohio.

In 1889 Garman (Bull. Mus. Comp. Zool. XVII., No. 6) gave an account of a blind

fish from some caves in Missouri. Mr. Garman says: "Compared with specimens from Kentucky and Tennessee, they agree so exactly as to raise the question whether the species was not originated in one of the localities and thence distributed to the others. ***There is no doubt that the representatives of Typhlichthys subterraneus in the various caves were derived from a single common ancestral species. The doubts concern only the probability of the existence of three or more lines of development in as many different locations, startfrom the same species and leading to such practical identity of result."

Ably arguing the case from the data on hand Garman came to the conclusion" that

these blind fishes originated in a particular locality, and have been and are being dis

*Contributions from the Zoological Department of the Indiana University, No. 27.

tributed among the caves throughout the eight specimens. I have since received an valley" (of the Mississippi).

Two of the specimens from Missouri served Kohl (Rudimentäre Wirbelthieraugen, 1892) for his account of the eyes of North American blind fishes. At my request Mr. Garman sent me two of the Missouri specimens. He urged me at the same time to make a more extensive comparison between them and the Mammoth cave specimens. A comparison of the eyes of specimens from the two localities not only proved that they represent distinct species, but that they are of separate origin. An announcement of the species without further description was published (Proc. Ind. Acad. Sci. for 1897, p. 231, 1898). The species was "named rose for the rediscoverer of the California Typhlogobius, a pioneer in the study of Biology among women,

additional number from a correspondent. From information gathered it would seem that this species (or similar ones) has a wide distribution in the subterranean waters of the southern half of Missouri and northern Arkansas, probably also the eastern part of Kansas.

On the surface the specimens very closely resemble Typhlichthys subterraneus from Mammoth cave, differing slightly in the proportion and in the pectoral and caudal fins. These fins are longer in rose. It is, however, quite evident from a study of their eyes that we have to deal here with a case of convergence of two very distinct forms. They have converged because of the similarity of their environment and especially owing to the absence of those elements in their environment that lead to external

[ocr errors]

FIG. 1. Side view of Troghlichtys showing the extent and distribution of the tactile organs.

Mrs. Rosa Smith Eigenmann." In the spring of 1897 I visited various caves in Missouri to secure additional material of what was recognized as in many ways the most interesting member of the North American fauna. No specimens were secured, but a liberal number of bottles of alcohol and formalin were scattered over the country. During the fall of 1898, through a grant from the Elizabeth Thompson Science Fund and through the courtesy of the officers of the Monon, the L. E. and St. L. and the Frisco R. R. lines I was enabled to visit the cave region of Missouri again. This time I visited nine caves and secured

protective adaptations. The details of the structure of the eyes of all the members of the Amblyopside will be published shortly, and I need call attention here only to the structures that warrant the conclusion that the cis- and trans-Mississippi forms of blind fishes without ventral fins are of distinct. origin. The blind fish Amblyopsis may be left out of consideration, since it is the only member of the family that possesses ventral fins. Otherwise, it would be difficult to distinguish specimens of similar size of this species from either subterraneus or rosa.

The eye of T. subterraneus is surrounded by a very thin layer of tissue representing

[blocks in formation]

descendant of a Chologaster. The intensity of coloration and the structure of the eye are the chief points of difference. The eye of rose is but about 1-3 the diameter of that of subterraneus, measuring .06 mm. or thereabout. It is the most degenerate, as distinguished from undeveloped, vertebrate eye. The point of importance in the present instance is the presence of comparatively enormous scleral cartilages. These have not degenerated in proportion to the degeneration of the eye and in some cases are several times as long as the eye, projecting far beyond it or are puckered to make their disproportionate size fit the vanishing eye. This species is unquestionably descended from a species] with well-developed scleral cartilages, for it is not conceivable that the sclera as found in Chologaster could, by any freak or chance, give rise during degeneration to scleral cartilages, and if it did they would not develop several sizes

*Kohl mistook the nature of these structures, as he did of every other connected with these eyes, except the lens and ganglionic cells.

too large for the eye. At present no known epigean species of the Amblyopsidæ possesses scleral cartilages. The ancestry of rosa is hence unknown. Amblyopsis possesses scleral cartilages and the eye of rose passed through a condition similar to that possessed by Amblyopsis, but the latter species has ventral fins and is hence ruled out as a possible ancestor of rosa. The epigean ancestry of Amblyopsis is also unknown. The ancestry of Typhlichthys being quite distinct from that of rose, the latter species may be referred to a new generic name Troglichthys.

Judging from the degree of degeneration of the eye Troglichthys has lived in caves and done without the use of its eyes longer than any other known vertebrate. (Ipnopes being a deep-sea form is not considered.) More than this, rose is probably the oldest resident in the region it inhabits.

Since the specimens kindly sent by Mr. Garman, in the course of examination have been reduced to sections, the specimens now in my possession, together with a few sent to the British Museum, all having come from the same cave, may be considered typical.

In addition to the acknowledgments made before I wish also to thank the officers of the Louisville and Nashville R. R. for transportation to Mammoth Cave. I must especially express my appreciation of the assistance rendered me by Mr. William McDoel, General Manager of the Monon, in enabling me to make explorations in the numerous caves of the Lost River region along his line and to visit caves at greater distances. Mr. H. C. Ganter, the manager of the Mammoth Cave Hotel, not only granted me leave to collect in the cave, but did everything possible to make my trip to this cave successful.

CARL H. EIGENMANN.

UNIVERSITY OF INDIANA.

[blocks in formation]

1. THE object of this memoir is twofold: first, to develop the theory of reproductive or genetic selection † on the assumption that fertility and fecundity may be heritable characters; and, secondly, to demonstrate from two concrete examples that fertility and fecundity actually are inherited.

The problem of whether fertility is or is not inherited is one of very far reaching consequences. It stands on an entirely dif ferent footing to the question of inheritance of other characters. That any other organ or character is inherited, provided that inheritance is not stronger for one value of the organ or character than another, is perfectly consistent with the organic stability of a community of individuals. That fertility should be inherited is not consistent with the stability of such a community, unless there is a differential death-rate, more intense for the offspring of the fertile, i. e., unless natural selection or other factor of evolution holds reproductive selection in check. The inheritance of fertility and the correlation of fertility with other characters are principles momentous in their results for our conceptions of evolution; they mark a continual tendency in a race to progress in a definite direction, unless equilibrium be maintained by any other equi

* Mathematical Contributions to the Theory of Evolution. Part I, Theoretical: By Karl Pearson. Part II, On the Inheritance of Fertility in Man: By Karl Pearson and Alice Lee. Part III, On the Inheritance of Fecundity in Thoroughbred Race-horses: By Karl Pearson, with the assistance of Leslie Bramley-Moore. Abstracts read before the Royal Society, December 8, 1898.

† I have retained the term 'reproductive' selection here, although objection has been raised to it, because it has been used in the earlier memoirs of this series. Mr. Galton has kindly provided me with 'genetic' and 'prefertal' selection. The term is used to describe the selection of predominant types owing to the different grades of reproductivity being inherited, and without the influence of a differential death-rate.

pollent factors, exhibited in the form of a differential death-rate on the most fertile. Such a differential death rate probably exists in wild life, at any rate until the environment changes and the equilibrium between natural and reproductive selection is upset. How far it exists in civilized communities of mankind is another and more difficult problem, which I have partially dealt with elsewhere.* At any rate it becomes necessary for the biologist either to affirm or deny the two principles stated above. If he affirms them, then he must look upon all races as tending to progress in definite directions-not necessarily one, but possibly several different directions, according to the characters with which fertility may be correlated-the moment natural selection is suspended; the organism carries in itself, in virtue of the laws of inheritance and the correlation of its characters, a tendency to progressive change. If on the other hand, the biologist denies these principles, then he must be prepared to meet the weight of evidence in favor of the inheritance of fertility and fecundity contained in Parts II and III of the present memoir.

2. The theory discussed in Part I opens with the proof that if fertility be a function. of any physical characters which are themselves inherited according to the law of ancestral heredity, then it must itself be inherited according to that law. As fertility would certainly appear to be associated with physique, we have thus an à priori argument in favor of its inheritance.

3. In the next place the influence of record' making on apparent fertility is considered. The mother with more offspring has a greater chance than one with fewer of getting into the record which extends over several generations, and, further, if every possible entry be taken from the

[blocks in formation]
« PreviousContinue »