'200 MISCELLANEOUS OBJECTIONS TO THE [Chap. VII. 



of service. With the poliinia of orchids, the threads which originally 

 served to tie together the pollen-grains, can he traced cohering into 

 caudicles ; and the steps can likewise he followed hy which viscid 

 matter, such as that secreted hy the stigmas of ordinary flowers, and 

 still subserving nearly hut not quite the same purpose, became 

 attached to the free ends of the caudicles ; — all these gradations 

 being of manifest benefit to the plants in question. With respect 

 to climbing plants, I need not repeat what has been so lately said. 



It has often been asked, if natural selection be so potent, why has 

 not this or that structure been gained by certain species, to which it 

 would apparently have been advantageous ? But it is unreasonable to 

 expect a precise answer to such questions, considering our ignorance 

 of the past history of each species, and of the conditions which at 

 the present day determine its numbers and range. In most cases 

 only general reasons, but in some few cases special reasons, can be 

 assigned. Thus to adapt a species to new habits of life, many co- 

 ordinated modifications are almost indispensable, and it may often 

 have happened that the requisite parts did not vary in the right 

 manner or to the right degree. Many species must have been 

 prevented from increasing in numbers through destructive agencies, 

 which stood in no relation to certain structures, which we imagine 

 would have been gained through natural selection from appearing 

 to us advantageous to the species. In this case, as the struggle 

 for life did not depend on such structures, they could not have 

 been acquired through natural selection. In many cases complex 

 and long-enduring conditions, often of a peculiar nature, are neces- 

 sary for the development of a structure ; and the requisite con- 

 ditions may seldom have concurred. The belief that any given 

 structure, which we think, often erroneously, would have been 

 beneficial to a species, would have been gained under all circum- 

 stances through natural selection, is opposed to what we can under- 

 stand of its manner of action. Mr. Mivart does not deny that 

 natural selection has effected something ; but he considers it as 

 " demonstrably insufficient " to account for the phenomena which I 

 explain by its agency. His chief arguments have now been con- 

 sidered, and the others will hereafter be considered. They seem to 

 me to partake little of the character of demonstration, and to have 

 little w r eight in comparison with those in favour of the power of 

 natural selection, aided by the other agencies often specified. I an; 

 bound to add, that some of the facts and arguments here used by 

 me, have been advanced for the same purpose in an able artick 

 lately published in the ' Medico-Chirurgical Keview.' 



