290 THE FOUR INSEPARABLE FACTORS OF EVOLUTION. 



17. A matter for investigation also is whether the development of function 

 invariably precedes the development of structure, whether physiological develop- 

 ment precedes morphological development, whether the evolution of function 

 precedes the evolution of structure. Take, for example, the evolution of the 

 horns in cattle; three distinct complexes of character are involved as follows: 



(a) Psychic, the desire to butt or use the horns. 



(b) Epidermal, the corneous sheath surrounding the horn. 



(c) The osseous protuberances of the skull. 



On the Lamarckian hypothesis the psychic desire to use the horn precedes 

 the development of the corneous sheath and of the osseous horn . In the actual 

 embryonic development the formation of the corneous sheath in the Bovidae 

 precedes that of the osseous horn. In the case of the genesis of the horns in the 

 titanotheres the first appearance is that of the osseous horn as a swelling; it is 

 impossible to say whether this structure was preceded by the psychic desire 

 to use a certain part of the skull in butting. In the development of cusps on the 

 molar teeth it would appear that these structures must precede the functions 



which they would subserve. 



Ontogeny, development and degeneration of parts, is generally found to 



precede development and degeneration in heredity. 



18. In general it would appear that the psychic evolution of habits must either be 

 coincident with or precede the morphologic evolution of organs, because most organs 

 in order to develop in ontogeny and come under the influence of selection or 

 elimination must first be selected or eliminated by habits in ontogeny. An organ 

 arising through heredity (a variation, mutation, saltation) but unused in the 

 course of the life of the individual could not have any utility value and therefore 

 would not be affected by selection. In this sense ontogeny plays an important 

 part in selection; that is, ontogeny is inseparable from selection. 



19. Fluctuations— It is important to note that certain fluctuations apparently 

 due to heredity may be due to ontogeny, that is, to causes favorable or un- 

 favorable affecting ontogeny of certain parts. Therefore it is difficult in many 

 cases to measure fluctuations as the expression of heredity and exclude the onto- 



genie influence. . 



20. Fluctuations in certain organs are not due invariably to hereditary fluctu- 

 ations in those organs, but to fluctuations in other organs. For example, con- 

 sider the occasional enlargement of the heart and arterial system as an hereaiW 

 fluctuation, which, for instance, in the case of the race horse "Eclipse, weigne 

 14 lbs., partly explaining the extraordinary endurance and speed of this annua . 



21. Correlation by somation adjustment or accommodation is a phenomenon 

 distinct from correlation by heredity; for example, Herbert Spencer cited cor - 

 lation of the muscles and bones of the neck in the great Irish deer Megaceros^ ^ 

 proof of the transmission of acquired correlated characters. The &1 ^ v ^ en ^ of 

 fallacious because similar correlation would be brought about m the nea hich 

 other deer by attaching a heavy weight permanently to the top of the head, w 



as 



