fiY R. J. TILLYARb. 397 



tremities; and also how, in the forewing, a portion of the fat- 

 body, lodged in the extreme base of the wing, got carried over 

 on to the wing wjien the cover-slip was let down upon it. Apart 

 from this, the residts obtained were quite satisfactory. 



The Mecoptera are generally regarded as being an extremely 

 archaic Order of Insects; and I'ightly so, for both in their general 

 structure and in their Palpeontological record, the evidence tends 

 to emphasise the fact that they are quite as old as any existing 

 Holometabola, if not older. Within the Order, the genus 

 Chorista is one of the most archaic types still extan^, and shows 

 close relationship to forms found in the Permian. I was there- 

 fore quite prepared, and indeed expectant, to find a very primi- 

 tive and complete tracheational development in the pupal wings 

 of this insect; and I was relying upon this to solve certain 

 problems concerning the fusion of some of the main veins near 

 the base of the wing, which cannot be determined with certainty 

 from the imaginal venation. But the result obtained was quite 

 different from what was expected; and, if there is any truth at 

 all in the Comstock-Needham Theory of Wing- Venation, we must 

 regard Chorista as a very highly specialised type in this one par- 

 ticular, if not in any other. 



The facts of the case can be gathered very readily from a 

 reference to the photomicrographs in Plate xliii., as well as the 

 drawings in Text-fig. 1. There are only tioo inain trachea' enter- 

 ing the winy-radiment. One of these belongs to the costo-radial 

 group, and passes into the main stem of the radius. In the fore- 

 wing, after giving off a very short and slender branch to R^, it 

 passes on along the radial sector. At the forking of Rs into 

 R2+3 and R4-f-5, it follows the upper branch, giving oft' a fairly 

 strong branch-trachea along the lower. Arriving at the forking 

 of R.^ from R3, it bends weakly down into the latter, and does not 

 reach the tip of the wing. The lower branch of this trachea passes 

 along Ri^o into R5, giving oft" a short branch to R4, and finally 

 ends up by bending down into Rgt- In the hindwing, there is 

 only a minute vestige of the branch into Rj. The main trachea 

 passes on into Rs; arriving at the fork of the sector, it gives oft' 



