432 CONCLUSION. Chap. XIV. 



dinatc to groups. Fossil remains sometimes tend to fill up 

 very wide intervals between existing orders. Organs in a rudi- 

 mentary condition plainly show that an early progenitor had 

 the organ in a fully-developed state ; and this in some instances 

 implies an enormous amount of modification in the descend- 

 ants. Tlnoughoiit whole classes various structures are formed 

 on the same ])attcrn, and at a very early age the embryos 

 closely resemble each other. Therefore I cannot doubt that 

 tlie theory of descent with modification embraces all the mem- 

 bers of the same class. I believe that animals are descended 

 from at most only four or five progenitors, and plants from an 

 equal or lesser number. 



Analogy would lead me one step further, namely, to the 

 belief that all animals and plants are descended from some one 

 prototype. But analogy may be a deceitful guide. Neverthe- 

 less all living things have much in common — in their chemical 

 composition, their cellular structure, their laws of growth, and 

 their liability to injurious influences. We see this even in so 

 trifling a fact as that the same poison often similarly affects 

 plants and animals ; or that the poison secreted by the gall-fly 

 produces monstrous growths on the wild rose or oak-tree. 

 ^Vith all organic beings sexual reproduction seems to be essen- 

 tially similar. With all, as far as is at present known, the 

 germinal vesicle is the same ; so that all organisms start from 

 a common origin. If we look even to the two main divisions 

 — namely, to tlie animal and vegetable kingdoms — certain low 

 forms arc so fiir intermediate in character that naturalists have 

 disputed to which kingdom they should be referred, and, as 

 Prof. Asa Gray has remarked, " tlie spores and other reproduc- 

 tive bodies of many of the lower alga3 may claim to have first 

 a characteristically animal, and then an unequivocally vegetable 

 existence." Therefore, on the principle of natural selection 

 with divergence of character, it does not seem incredible that, 

 from some such low and intermediate form, both animals and 

 plants may have been developed ; and, if we admit this, we 

 must likewise admit that all the organic beings Avhich have 

 ever lived on this earth may be descended from some one pri- 

 mordial form. But this infei'ence is chiefly grounded on anal- 

 ogy, and it is immaterial whether or not it be accepted. No 

 doubt it is possible, as Mr. G. H. Lewes has urged, that at the 

 first commencement of life many difl'erent forms were evolved; 

 but if so, we may conclude that only a very few have left modi- 

 fied descendants. For, as I have recently remarked in regard to 



