No. T.] ROBINS — NATURAL iSELECTION. 417 



ranging through so vast a scale of being, that it is possible to 

 connect by gradations almost imperceptibly progressive the lowest 

 with the highest form of each function and organ. 



For example, the eye is a most complex, delicate and efficient 

 organ, replete with admirable adjustments and adaptations, yet 

 of its genesis by evolution a plausible account may be given. 

 We can trace the beginning of the function in that sensibility 

 to the presence or absence of light which is exhibited in the 

 whole mass of the humblest protozoan forms. To them their 

 rudimentary and vague appreciation of alternate sunshine and 

 shadow, scarcely to be called vision, is doubtless useful for the 

 avoidance of danger, and every stage of advance in quickness 

 and precision must give increased advantage in escaping from 

 peril and in the procurement of food. And, finally, the compara- 

 tive anatomist may trace for us the several gradations, insensibly 

 blended, by which we pass from a few pigment cells on the 

 swimming disk of a medusa up to the most fully developed organ 

 of sight in the vertebrate sub-kingdom. Wide as is the interval 

 between tho eye-speck of a radiate and the human eye, that in- 

 terval may be filled by the selection of a continuous, advancing 

 series of slowly difi"ering forms, such a series as must have united 

 the extremes, if all the structures had originated by descent with 

 accumulated minute modifications from a protozoan ancestry. 



Not more difficult will be the task of accounting for the pro- 

 gressive development of any of the remaining common functions 

 of life whether animal or vegetable. They are all represented in 

 a rudimentary manner in the lowest forms of life. They all are 

 profitable to the possessor, and increasingly profitable with in- 

 creased specialization of the function and development of its 

 organs. And, finally, from the boundless diversity of nature it 

 is possible to choose forms which may be arranged in lineal series, 

 exhibiting the links which may be supposed to connect the sim- 

 plest with the most highly organized manifestation of the function- 

 But if there be in nature any organ which does not now exist 

 in a rudimentary form anywhere, and of which nature furnishes 

 no evidence that it ever did exist in a rudimentary form, then 

 it is obvious that evidence of its development through evolution 

 is wanting. And if, further, it is impossible to conceive that 

 the function could ever usefully exist in the rudimentary condi- 

 tion, we are compelled to say that we cannot conceive how such 



Vol. IX. AA No. 7. 



