HISTORY OF ZOOLOGY 47 



help of the struggle for existence, to explain tlie phylogenesis of organ- 

 isms. (Neo-Lamarckism.) 



Influence of Environment.— To what extent can the environment 

 directly bring about a permanent change in the structure of plants and 

 animals? To decide this is no simple proldem, on account of the com- 

 plexity of the factors entering into the question. 



In cases where the food-supply is altered, organisms change in a very 

 remarkable manner and within a short time; but these changes (Nageli's 

 ' Modifications through Nutrition ') seem to have no permanence. Plants 

 which, found in nature in poor soil, are transplanted into rich soil, or 

 vice versa, soon acquire quite a different appearance, and preserve this 

 through the following generations, so long as they remain in the rich soil ; 

 but the plant quickly returns to its former appearance when replaced in 

 its previous surroundings. 



In general, a change seems to be the more permanent the more slowly 

 it has developed. In researches upon the influence of environment, it is 

 better to experiment with slowly-working factors, such as hght and heat, 

 dry or moist air, different intensities of gravitation, of stimuli, etc., which 

 can be excluded from the environment of the organism. In this way 

 positive results seem to have been attained. WTien pups of ]'anessa 

 urtica and Arctia caja are reared in the cold (down to — 8^C.) the butterfly 

 or moth which escapes is more or less conspicuously modified, the male 

 the more. If these altered males and females be used for further breeding, 

 a part of the male oflfspring will have the cold markings, even if reared in 

 the normal conditions. It is however probable that in these cases the 

 cold had a direct effect upon the germ cells from which the aberrant indi- 

 viduals arose. The results of Tower in breeding potato-beetles are in the 

 same direction and are even more conclusive as to the modification of the 

 germ cells. 



Use and Disuse. — Regarding the efficiency of zise and disuse, there 

 is no doubt that an animal is influenced to a great extent by the manner in 

 which the organs are used. The organs which are much used become 

 strong and those which are not used Ijecome weak. The only question is 

 whether these, in the strict sense of the word, newly-acquired character- 

 istics are transmitted to the offspring, or whether the descendants, in 

 order to attain to the same condition, must repeat in the same way use and 

 disuse. In the latter case the cumulation of characteristics, and with it 

 the possibility that these may become permanent, is excluded. It is to be 

 regretted that accurate results are still lacking on a point so well adapted 

 for experimental treatment. At this time rudimentary organs strongly 

 favor the Lamarckian principle ; for we see that cave animals, which for 



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