234 NATURAL SCIENCE [April 



These two factors I take to be amply sufficient for the whole 

 of the evolution of plant structures, without any aid from 

 Natural Selection whatever" (p. 32, "Origin of Plant Struc- 

 tures "). 

 Cope. — " Many of the zoologists of this country, in common with 

 many of those of other nations, have found reason for believing 

 that the factors of evolution which were first clearly formu- 

 lated by Lamarck are really such. This view is taken in the 

 following pages " (" Primary Factors of Organic Evolution." 

 E. D. Cope). 



To summarise these various positions : — 



Henslow considers that the sole factors in the formation of species 

 are the direct action of the environment and the responsive 

 power of protoplasm, and that Natural Selection is of use 

 only in so far as it is able to select the vigorous, solely on 

 account of their being so, but has no power to select and 

 develop any particular portion of an organism separately. 



Cope, who, while largely agreeing with Henslow's position, con- 

 siders Natural Selection a subsidiary factor in the formation 

 of species. 



Darwin, who considered Natural Selection to be the main factor in 

 developing species, but considered variations as due largely to 

 the direct action of environment, Natural Selection subsequently 

 developing variations so produced, also considered that changed 

 environment could modify directly the reproductive system 

 and hence influence heredity. 



Weismann, who believes that use - inheritance plays no part in 

 species formation, and extends the action of Natural Selection 

 to the biophors, etc. Natural Selection and indefinite vari- 

 ability are therefore the only factors in evolution. 



In criticising the position of the Neo-Lamarckians, I shall mainly 

 base my arguments on Professor Henslow's position, because he has 

 taken the most definite, and at the same time the most extreme, 

 position. I do not wish to be understood to doubt the facts 

 adduced, or even to assert that the conclusions drawn are incorrect, 

 but simply to show that the facts as stated, and the arguments 

 drawn from these facts, do not on logical grounds prove the position 

 taken up. 



I shall choose for the statement of his views the epitome given 

 in the preface to " Origin of Plant Structures," because it is the 

 most condensed statement of his position, and appears to accord 

 fully with an article contributed to this journal at a later date 

 (September 1897). 



