23 



nates and becomes an elevation as soon as this obstacle is removed. 

 This explains the so-called ^vorzeitige Entwicklung'' (premature 

 development). 



Consequently in the beginning the wing-rudiment is not connected 

 with the tracheae and in instar 1 the rudiment of the wing is 

 only a minute thickening of the hypodermis. This knowledge will 

 be uf much use to us in discussing the so-called rudimentary 

 stigmata on the mesothorax and roetathorax. 



The way in which the thorax is provided with stigmata is a 

 second point which I wish to discuss. There are many different 

 opinions on this subject. 



In his description, which for the rest is exceedingly accurate, of 

 CoAsun (Traite de la chenille, 1760) Lijonet does not mention the 

 rudimentary thoracic stigmata. The remaining stigmata he points 

 out very accurately and also their connection with the „bronchi" 

 as he calls the tracheae. It is peculiar that he does not fully 

 believe in their respiratory function in consequence of the 

 experiments mentioned by him on p. 78. 



A. C. OuDEMAKs observed (1886, p. 19) that the Myriapodae 

 and Hexapodae always bear the stigmata within the limits 

 of the segment itself, but he admits that in adults they can be 

 shifted either to the front part of the segment or to its back part 

 and in so doing may even get into the intersegmental membrane. 



In direct opposition to this stands Henneguy's contention (1904) 

 that the stigmata generally occur intersegmentally, but that later 

 on this position may be altered. He ascribes this to the compli- 

 mentary segments which Kolbe discovered. This writer says that 

 in the beginning no stigmata occur on the head and the protho- 

 rax (1. c. p. 20). With this the models of Hydrophilus piceus L. 

 (manufactured in the studio of Ziegler according to K. Heider's 

 treatise, 1889) are in perfect harmony. Here it is clearly visible 

 that the first stigma appears on the mesothorax (Stage 9, model 9). 



For a student, who has not yet undertaken any special investi- 

 gations in this direction, it is exceedingly difficult to find out 

 the truth. A priori one would be inclined to think that both 



