( fxi ) 



apply not only to the thought of Lamarck but to those of 

 many modern naturalists as well, and because, so far as I am 

 aware, no attempt has been made to meet the objection. In 

 its most condensed form the argument may be stated thus : — 

 Lamarck's " first law assumes that a past history of indefinite 

 duration is powerless to create a bias by which the present 

 can be controlled ; while the second assumes that the brief 

 history of the present can readily raise a bias to control the 

 future.* 



I now pass to the discussion of evidence derived from 

 the study of the insect world. 



I do not propose to multiply examples, but shall be content 

 with a few of those w^hich seem sufficiently well adapted to 

 illustrate the main lines of evidence. They have been chiefly, 

 but by no means invariably, selected from the Lepidoptera. 

 This is merely due to the accident that my experience has 

 been chiefly gained in this Order, and not because the examples 

 are in any way moi-e suitable or convincing than those of other 

 Orders. As regards the most interesting part of the discussion, 

 that relating to instinct, the most striking examples have of 

 course been chosen from the Hymenoptera. 



The origin of the inijml groove lohich receives the silken looj) 

 in Pierinse, etc. — If we examine the doi-sal surface of such 

 a Pierine butterfly as Pieris brassicee or ra2)ss it is at once 

 seen that the first abdominal segment is traversed by a strongly 

 marked line parallel with its posterior boundary. This 

 character is so well marked that it presents all the appear- 

 ance of a morphological feature. 



A study of the living suspended pupa shows that the line 

 is formed by the approximated lips of a groove which receives 

 the silken loop or "girdle" as it is often called. Longitu- 

 dinal vertical sections of the dorsal cuticle are of course 

 transverse to the line, and reveal the fact that the bottom 

 of the groove is specially thickened. Here was a feature at 

 first sight strongly suggestive of the mechanical effects of 

 linear pressure, pointing to an origin in a kind of mutilation 

 performed by the silken cord upon the soft freshly-exposed 

 surface of the pupa. When I found that removal of the loop 

 * " Nature," vol. li, 1894, p. 127. 



