ORIGIN OF APPARENT MUTILATION 147 



relating to Instinct, the most striking examples have of 

 course been chosen from the Hymenoptera. 



The Origin of the Pupal Groove which receives 

 I he Silken Loop in Pierinae, &c. 



If we examine the dorsal surface of such a Pierinc 

 butterfly as Pieris brassicae (the ' Large Garden White ') 

 or P. rapae (the ' Small Garden White ') 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 

 appearance 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. 

 Longitudinal 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 mechani- 

 cal 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. W^hen 

 I found that removal of the loop before pupation, but 

 after the period at which the larva could spin another, 

 did not alter the normal appearance of line and groove 

 in the resulting pupa, I was for the moment convinced 

 that acquired characters are hereditary. But fortunately 

 the inquiry did not come to an end at this point. It was 

 observed that the Pierlne pupae which furnished the 

 material for experiment {P. brassicae or P. rapae) Invari- 

 ably suspended themselves either horizontally or verti- 

 cally with the head upward, — never vertically with the 

 head downward. Several larvae of P, brassicae had fixed 

 themselves in the normal vertical position preparatory to 

 pupation, upon a sheet of glass. Before pupation, but 

 after the period at which the larvae could fix themselves 

 afresh or Indeed make any attempt to spin, the glass 

 sheet was rotated through half a circle, so that all the 

 larvae came to be suspended head downward. In this 



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