190 The Science of Life. 



On the other hand, and of more biological importance, 

 there is the action of the environment upon organisms. 

 This formed the main subject of Prof. Karl Semper's 

 masterly Lowell Lectures in 1881, and his book should 

 certainly be ranked first in the literature of the subject. 

 If we add to that the records of a representative series 

 of experiments, such as those of Professor Weismann 

 on the seasonal dimorphism of butterflies, of Professor 

 Poulton on the coloration of caterpillars, of Dr. De 

 Varigny on the dwarfing of water-snails (Limnceus), of 

 Profs. Born and Yung on the determination of sex in 

 tadpoles, and similar experiments by M. Maupas and 

 Prof. Nussbaum on the rotifer Hydatina senta\ and 

 finally read Prof. Weismann's Romanes Lecture, we 

 gain a fair idea of the present state of knowledge and 

 opinion on the subject. 



As the result of much detailed work, biologists have 

 become clearer as to the complex relations between 

 organisms and their environment. A summary may be 

 attempted here. 



(1) There is the relation of normal functional depend- 

 ence, in virtue of which life continues from moment to 

 moment, as may be illustrated by the respiratory inter- 

 change of gases. Of the same sort, obviously, is the 

 relation between the developing embryo and its environ- 

 ment, including not only the essential food-supply, but 

 various external stimuli, such as gravity, pressure, the 

 chemical medium, heat, light, and electricity. 



(2) There is the relation of direct modification, wherein 

 an environmental change produces a change in the meta- 

 bolism of the organism which is followed by a lasting 

 change of structure. There must always be some change 

 of structure, but if this passes what may be called the 

 limit of vital elasticity the result is a " modification " 

 which persists. The Lamarckians believe that these 

 modifications of the body may affect the germ-cells in 

 such a way that the offspring may show a change in the 

 same direction as the original modification, and apart 

 from the recurrence of a similar environmental influence, 

 This remains a hypothesis, and there are few facts at 

 present known which can be said to favour it. 



