Page:The New International Encyclopædia 1st ed. v. 07.djvu/374

* EVOLUTION. 326 EVOLUTION. acclimatized, and in five months more the tem- perature was gradually raised to 78°. These experiments were continued until the tempera- ture of 158° F. was reached, when an accident put an end to the experiments, and the new race thus adapted became extinct. Another instance of the effects of changes in temperature is the ease of a pond-snail [Physa which lived in the water of an artesian well with a temperature of 32° to 33° C. (c.90° F. ) : they were dwarfed and frequently deformed, but they reverted to their normal size when, owing to the diminution of the supply, the water became cooled at the end of two years. Owing to the great summer heat (104° F.) in the Transcaspian oasis, birds mult in summer. Dolbear states that the rate of the chirp of the cricket is entirely determined by the tempera- ture; at 60° F. the frequency is 80 times a minute, and at 70° it. chirps 12p times a minute. Wasmann was able during three successive winters to induce parthenogenesis in the workers of an ant [Formica sanguined), and in their helpers or slaves, by artificially warming the nests. On one day as many as twelve workers of this ant were seen laying eggs. Most of them were large workers, but small ones were also affected, and the smaller the ant the more tedious was the process of egg-laying. Of many hundreds of eggs thus laid none attained full development, as the eggs or larva 1 were all de- voured by the ants. Many mollusks common in France bee e in Africa (Algeria) doubled in size, while Bulimus deeollatus becomes even nine times larger than in Europe. On the other hand, cold is an efficient agent in modifying plants and animals. It is well known thai fishes, caterpillars, etc., can be frozen, and, i initially thawed out, become again active, Om "i thi cabbage butterflies [Pieris bra&sica) may live through — 20° C, and the European garden snail (Helix pomatia) survives refrigera- tion to 130° C, the lowest temperature which could be obtained (Yung). As is well known, the cold of highlands and of mountains, as well as an extreme northern climate, dwarfs man and animals as well as plants, while the proportions of the body are also changed. Salamanders, like the axolotl of Mexico, and the siredon of Lake Como, Wvo.. under the influence of the eleva- tion and low temperature, become retarded in their development : while the reproductive organs become accelerated in development and they while in the larval state. Parthenogene sis in aphids ceases at the approach of the autumnal cold. i soi Change of Climate. This has a much greater effeel on the original ion of varieties and species than is generally supposed. It was formerly the fashion to claim lliat climate had little or nothing to do with the origination of pi : II is not improbable, however, thai near- ly a third or a half of the s] ies in museums, or of those described in biological literature, are i limatii or local varieties or species. The study < .i rried on, by measurements mbers of specimens, shows I bal each however limited, has its local rac each "f which differs from the others in slight vet con 'nil features. iel on general i-i inciples ii is a change in t he eon, lit ion- of life. i- slight, which react- on the organism, and results in adaptation to tin- environment. Local varieties are usually restricted to small circumscribed areas, separated by mountains, or by altitude, or by moist or dry regions; or. if marine, by different kinds of bottom, whether sandy, muddy, or rocky, or by different degrees of saltness of the water. In the fresh-water fishes of the Pacific Slope each locality has its peculiar variety, which, in the aggregate, is different from the variety of every other locality (Gilbert an.l Evermann). These variations are due to the different environ nient, for the differences in temperature, altitude, and topography in the course of the different streams which take their rise in the Sierra Nevada are very marked. Indeed, whether we consider the insects, ti-h <•-, birds, or mammals in such a region as the Pacific Coast, which is undergoing rapid erosion or base-leveling, the number of local races, or, as some prefer to call them, local species, is remarkable. Packard has observed that species of moths which do nut vary much on the Atlantic coast, where the topograph- ical conditions are more stable, are in California exposed to very considerable variation. Even in two neighboring lakes in Indiana (Lakes Turkey and Tippecanoe) the individuals of a darter (Ethroslomn capsodes) from one lake differ constantly from those of the other lake in color, in the scales of the nape, and of the lateral line, in the number of spines in the anal fin. in the number of dorsal spines and rays I Moenk- haus). Similar instances are the ahsence of ven- tral fins in some of the fishes inhabiting even widely separated mountain lakes, and the pres- ence of enlarged scales along the base of the anal fin in the eyprinoid fishes inhabiting the moun- tain streams of India; also the peculiar color patterns of the fishes in certain portions of north- ern Georgia See Isolation. Introduced species tend to vary much more than in their native lands. Children horn of British, German, or French parentage become in the United States slightly taller than their parents; the soldiers of the United States Army during the Civil War of 1861-65 were found, by measurements made on 1.110. out) individual-, to average taller than those of the British Army. Dr. Bumpus has critically examined and meas ured over 1700 eggs of the English sparrow, one- half from England and the other half collected at Providence, B. I. He found that the eggs of the new or American race or breed vary much mure than the European, differing in being smaller and of a strikingly different shape, being more rounded, and with a greater amount of color variation. His measurements of the European periwinkle [lAttorina littorea), 3000 from Eng- land, and 3000 from New England, afforded simi- lar results. Since its' introduction, about 1855, into the Bay of Chaleurs and its rapid spread along the coast to New York, this little mollusk has lergone a transformation adapting it to the di Here nt conditions of our northeastern coasl It has become more elongated, lighter in weight, more bulky, and th lor markings arc less pronounced. Also large collections, in some cases 1000, from Casco Bay, Wood's Hole. Seaconnct. Newport, and Bristol, were found lo present constant variation- at each locality, the curves oi variation exhibited on the charts prepared by Dr. Bumpus being different for each locality. Su ii is with a European land snail i //■ oralis) introduced within a few year-