Another instance of the effects of changes in temperature is the ease of a pond-snail (Physa acute) 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 hdat (104° F.) in the Transcaspian oasis, birds molt in summer. Dolbear states that the rate of the chirp of the cricket is entirely determined by the tempera ture; at 6'0° F. the frequency is 80 times a minute, and at 70= it chirps tine's a minute.
Wasmann was able' during three successive winters to induce parthenogenesis in the workers of an ant (Formica sanguince), 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, hut 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 larvm were all de voured by the ants. Alany mollusks common in France become in Africa (Algeria) doubled in size, while Da/imus dceollatus 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 that fishes, caterpillars. etc., can be frozen, and, if gradually thawed out, become again active. One of the cabbage butterflies (Picris brassica) may live through —20° C., and the European garden snail (Helix pometia) 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. Wyo., under the influence of the eleva tion and low temperature. become retarded in their development: while the reproductive organs become accelerated in deve.opment and they breed while in the larval state. Parthenogene sis in aphids ceases at the approach of the autumnal cold.
ErrEcrs OF CTIANGE OF CLIMATE. 'Phis has a much greater effect on the origination of varieties and species than is generally supimsed. It was formerly the fashion to claim that climate had little or nothing, to do with the origination of species. It is not improbable, however, that near
ly a third or a half of the species in museums, or of those described in biological literature, are climatic or It/Ca 1 varieties or species. The study of variation as now earried on, by measurements of great numbers of specimens, shows that each legion, however limited, has its local race or breed. each of which differs from Or others in slight yet constant features. And on general prineiples it is a change in the conditions of life, however slight. which reacts on the organism, and results in adaptation to the 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-wate• 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 and Eve•mann). These variations are due to the differept environ ment, 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 inseets, fishes, 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 not 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 (Etheostome 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 (Moenk haus). Similar instances are the absence 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 cyprinoid 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.