THE CONDITIONS OF LIFE IN ANIMATED BEINGS. 



421 



ment in animals, demonstrating identity of origin 

 for all, revealing the most curious details upon 

 the changes that occur in the organs, and in the 

 conditions of existence of a multitude of species, 

 making the most instructive comparisons between 

 the permanent and the transitory states of an 

 immense number of creatures, have greatly en- 

 larged the horizon of philosophy. 



Thus we have reached an epoch in which 

 science, rich in solidly -established truths, has 

 assumed a character of remarkable grandeur. 

 Aided by the very various methods which inves- 

 tigators have employed, we are certain of yet 

 making great and numerous discoveries, of com- 

 pleting many branches of knowledge that remain 

 imperfect, and of attaining new generalizations ; 

 but a different view is coming into notice of those 

 which have hitherto served as guides to natural- 

 ists, promising to carry our resources to the 

 highest degree of availability in the examination 

 of the phenomena of life. Although by itself 

 alone the comparative study of apparatus may 

 fail to enlighten us as to the object of certain 

 modifications, or to explain the reasons for vari- 

 ous changes in forms, in arrangements, in the ex- 

 cessive development or the atrophy of certain 

 parts, and although experimental research, in its 

 turn, owing to the necessity that confines its 

 action within rather narrow limits, may also be- 

 come impotent, yet the resources of the scientific 

 spirit will not be exhausted. There will still re- 

 main to be followed that which we may call ex- 

 perimenting on Nature. In a word, the solution 

 of the highest problems of natural history must 

 be looked for in the constant observation of the 

 coincidences between all the details of organiza- 

 tion and the vital conditions in the case of each 

 animal. Nothing exists in the organism, it seems, 

 without having some duty to perforin. To this 

 rule we perhaps find a single exception : certain 

 parts, dependent on the teguments which are 

 strongly developed in males and wanting in their 

 females, are probably nothing more than orna- 

 ments. 



No zoologist of the present day takes con- 

 formity of abode and of aptitude as an assured 

 sign of essential resemblances ; and yet, in conse- 

 quence of the tendency we have remarked, this 

 sometimes leads to serious mistakes in judgment. 

 One of the most wonderful things in Nature is 

 the extreme diversity gained from a common 

 stock — a diversity which displays itself, in the 

 case of living beings, both in their characteristics 

 and in the circumstances of their lives. A varia- 

 bility in conditions of existence which is often 



wide in species of the same natural group, a sort 

 of repetition of similar conditions in species of 

 groups more or less unlike, carry this diversity to 

 the farthest imaginable limits. Hence come 

 special applications of important characteristics 

 in the organism. 



The idea of the relation existing between 

 peculiarities of conformation and the kind of life 

 will be made more precise by an instance readily 

 understood. Every one has heard of those dis- 

 tinctions between granivorous and insectivorous 

 birds that belong to a science now obsolete. The 

 sparrow, the chaffinch, and goldfinch, are thought 

 to be granivorous ; the warbler and wagtail are 

 classed as insectivorous, notwithstanding their 

 mode of feeding, which is less exclusive than was 

 once supposed. All these birds show absolutely 

 the same general structure; those marks which 

 are distinctive at a glance, as the shape of the 

 beak, are quite of a secondary order, and merely 

 denote adaptation to biological circumstances 

 very slightly different. Other species of birds, 

 which are almost sisters in their habits, yet of re- 

 motely separate origin as regards their general 

 organization, present certain superficial traits of 

 resemblance that easily mislead observers dis- 

 posed to trust to appearances. Every one knows 

 the difference between little swallows— the win- 

 dow-swallow, the chimney - swallow, the bank- 

 swallow, and the great swallow, or martin — but 

 every one also, including many naturalists, is con- 

 vinced that all these birds, called by one and the 

 same name, belong to the same family. Yet this 

 is not so at all ; the little swallows have the con- 

 formation of sparrows, and their adaptation to a 

 rather peculiar kind of life is almost all that 

 makes the difference. The great swallow is con- 

 structed in an altogether different way, and shows 

 a remarkable affinity with those charming birds 

 of Southern America called humming - birds. 

 Both little swallows and great swallows, repre- 

 sentatives of separate and strongly-characterized 

 types, feed alike on insects which they snap up 

 on the wing ; then, too, they are alike in having a 

 small beak, broad at the base and cleft down to 

 below the eyes ; intended alike to sweep through 

 the air swiftly and to traverse great spaces, they 

 are similar in having the quill-feathers of their 

 wings extraordinarily long. Thus, the species of 

 a great number of natural groups, offering greater 

 or less dissimilarity in their kind of life, are re- 

 marked for very evident peculiarities, though of 

 a secondary order, which fit them properly for 

 fixed conditions of existence. Therefore, species 

 of groups that are wholly distinct may resemble 



