INTRODUCTION. lix 



ing herb or tree to relieve the monotony of the rank, weedy, colossal, but unfinished 

 plants clothing the hills and plains of those days. 



Thus the whole course of development was from crude, chaotic, generalized 

 forms, both animal and plant, to more elaborate, highly-finished, or specialized forms ; 

 this progress towards higher and better things biological going on hand in hand with 

 progress in continent-building, the elaboration of lowlands, plateaus, and mountain 

 chains, until, in the fulness of time, the whole creation revels in marvels of beauty, 

 in a variety so beautiful and delicate as to appeal to the aesthetic tastes and to form a 

 training-school in the good, the beautiful, and true for the last product of evolution, 

 that being who has been endowed with sufiicient intelligence to read the history of 

 creation, and to look up beyond and above the material world to the Infinite Source of 

 all the physical and evolutional forces which have made the universe. 



The facts and inductions we have hastily glanced at were established before Dar- 

 win published his Origin of Species. The interpretation now given to them is 

 mainly due to him, who has shown their full significance. As full proofs, however, are 

 the facts regarding the conditions of existence which have been mostly collected by 

 those to whose works we have already referred. These, in the main, are the influence 

 of light or its absence, temperature, parasitism, etc. 



The study of the effect of these physical agents on organisms is still in its infancy; 

 the facts can best be observed in external nature, and experimentally in the laboratory. 

 As the result, however, of known facts, it seems evident that the causes of variation, 

 manifold as they seem to be, are such as to be appreciated by the patient and careful 

 observer, and this is the direction which biological research is now taking. Changes 

 in the environment and adaptation to such changes as these, then, are the fundamental 

 causes of the origin of new forms of life. 



The next factor is the transmission to the offspring of changes thus induced, and 

 to which the organism has become in a slight degree adapted. This is heredity. 



Of the causes of heredity we know almost nothing. The solution of the problem 

 belongs to the future. The facts are witnessed by every human being. All organisms 

 transmit their own peculiarities as well as those of their race, variety, species, genus, 

 or class to their offspring. Heredity is seen externally in the general shape of the 

 body or trunk, whether stout or slender ; in the head and in the limbs, even in the 

 nails and hair, also in the human countenance, in the expression or charactei-istic fear 

 tures, as well as in the skin. The Romans, says Ribot, had their Nasones, Labeones, 

 Buccones, Capitones, and other names derived from hereditary peculiarities. Internal 

 peculiarities, such as the shape and size of the bones of the skeleton, and especially 

 the skull and teeth, are hereditary, and even, says Lucas, the heredity of excess or de- 

 fect in the number of the vertebrae and the teeth has been observed. The circulatory, 

 digestive, muscular, and nervous systems obey the same laws, which also govern the 

 transmission of the other internal systems of the organism. There are some families, 

 says Ribot, in which the heart and the size of the principal blood-vessels are naturally 

 very large ; others in which they are comparatively small ; and others, again, which 

 present identical faults of conformation. The general dimensions of the brain, and 

 even the size and form of the cerebral convolutions, as observed by Gall, are hereditary, 

 and this author in this way accounted for the transmission of mental faculties. Pecu- 

 liarities in the blood-vessels and the blood itself may be transmitted, as seen in the ten- 

 dency in certain families to apoplexy, haemorrhages, and inflammatory diseases. 

 Length of life, fecundity or the opposite trait, is hereditary. In some families the hair 



