304 



The opinions of the investigators differ very much on the 

 meso- and the metathorax, as may be seen from Fracker's list 

 (1915 1. c. p. 40), from the figures arranged by me on plate X 

 and from the example on page 38. 



I tliink that the cause of the difference between type II and 

 type I must be sought in the shifting of the stigmata and in 

 their final disappearance later on. 



On the meso- and the metathorax one generally finds three 

 setae at the oral border of the segment, mostly arranged in one 

 vertical line. 



About in the same row, but sometimes a little in front of it 

 or behind it, is another seta, and behind this one we often find 

 a peculiarity of the surface of the skin. Sometimes in the shape 

 of a pigmental spot (e.g. Porthesia clirysorrhoea^ Zeuzera pyrhia)^ 

 another time in that of a verruea (e. g. Ar et ia caja^ Sericinus 

 telamon)^ or as a distinct dilatation of the system of air-tubes, 

 which is seen through the transparent skin (e. g. Piens hrassicae 

 and P. napi). These variations of the surface of the skin I take 

 to be caused by the wing-rudiment (Boas 1899), but, as it is situated 

 on the place originally occupied by the stigma, the seta which is 

 placed in front of it keeps its character as .s\ prostigmalis. On 

 this point I agree with Quail, who calls it III B. Under this 

 seta stands another one, and over the base of the leg, one more. 

 All these six setae are situated in one vertical row. This type seems 

 therefore to be very primitive. But having seen that type Ia and \h 

 are pseudo-primitive and after having expiained in chapter IV that 

 the thorax is generally of a secondary construction, I think an- 

 other point of view may also be taken. 



The uppermost seta does not give any difficulties, and may 

 safely be considered to be s. dorsalis^ and the fourth .s-. prostig- 

 malis. In this case it is clear, that the two last setae are 

 s. infrastigmalis and 8. hasaJis and that the third of the row is 

 s. siqrrastigmalis. There remains still one seta, namely the second 

 of the row. 



It can be easily understood that this seta is considered by many 



