394 LAND ANIMALS 



the temperature, and investigators like Wallace and Heilprin, who 

 based their conclusions concerning the factors causing animal distribu- 

 tion primarily upon studies on birds and mammals, naturally con- 

 cluded that climate is not closely correlated with animal distribution. 57 



The means for controlling body temperature are quite differently 

 developed in different animals so that all gradations of temperature 

 limitations are found in the mammals and birds as well as in the 

 poikilothermal forms. Vultures, buffaloes, giraffes, dwarf musk deer, 

 hippopotami, and the anthropoid apes are examples of stenothermal 

 warmth-limited animals. Polar and alpine animals tend to be steno- 

 thermal cold-limited forms. The principle of Bergmann applies only to 

 homoiothermal animals. Poikilothermal animals generally attain 

 larger size in warmer climates. This applies to insects 58 (with the ex- 

 ception of the arctic bumblebees, cf. Chapter XXV), tree frogs, toads, 

 and reptiles among the land animals. 



Temperature also has an effect on the coloring of animals, as may 

 be gathered from the appearance of the seasonal dimorphism of the 

 butterflies and certain other insects. This influence is by no means uni- 

 form; the heat may cause dark coloring, as in Polyommatus phlaeas, or 

 bright coloring, as in the species of Papilio. Final decision concerning 

 the factors which produce color varieties in the various climates can 

 be arrived at only by experimentation, because of the complexity of 

 the intermixture of hereditary and environmental conditions and be- 

 cause of the variety of effects produced by different combinations of 

 climatic factors. Such experiments have been made most extensively 

 upon butterflies. Through the effect of raised or lowered temperatures 

 upon the pupae, directly after pupation, wing colors have been pro- 

 duced in many central European butterflies that resembled the colors 

 of the southern or northern varieties of the species. Thus, the effect of 

 high temperatures on Polyommatus phlaeas was the production of 

 dark specimens like the variety eleus that occurs at Naples; the second 

 generation of German swallowtails, Papilio machaon, can be so altered 

 by heat as to resemble the Syrian form of this species. Exposing the 

 small butterfly Vanessa urticae to warm temperature produces a vari- 

 ety similar to ichnusae, which lives in Sardinia; exposure to low tem- 

 perature produces the variety polaris, found in Lapland. The Apollo 

 butterfly (Parnassius apollo) changes to the dusky mountain form 

 brittingeri through the effect of cold. 



By comparing the colors of related birds from different climates one 

 may arrive at an analysis of the effects of temperature. 59 The pigments 

 of feathers (melanin and lipochrome) may be distinguished by their 

 reaction to different temperatures. Melanins (black, brown to clay- 



