154 Knaiyweed Gall-jiif 



the area round the mouth is changing to a reddish-brown colour; and 

 undergoing chitinisation. A series of fine grooves which radiate in 

 a backward direction from the mouth are very apparejit about this 

 stage. These grooves or striations are present on younger larvae 

 (Aug. 22nd) but in order to see them it is necessary to strip off the cuticle 

 from the anterior part of the body and examine it under the microscope ; 

 this area is not chitinised in larvae at this stage ; in those larvae, however, 

 where this area has become chitinised the grooves can be much more 

 easily seen. A series of small channels at the sides of the oral lobes 

 in the larva of Musca domeslica L. is described and figured by Hewitt 

 (1908). The grooves referred to above may correspond to those of the 

 house-fly larva. 



The first appearance of the chitinised area round the mouth aperture 

 probably coincides with the nearly completed feeding period. From 

 mid-September to early October the majority of the larvae are fully 

 fed, and they remain head downwards in the larval chambers until 

 pupation commences in the following spring ; the larvae reverse their 

 position just before pupation. During the period of feeding, and the 

 growth of the gall, an opening of the larval chamber to the exterior 

 is maintained, and this opening is sufficiently wide to allow the imago 

 to emerge ; this opening is situated at the apex of the chamber and 

 is much narrower than the basal part in which the larva hibernates. 



The fact that the larva remains head downwards with the strongly 

 chitinised posterior segment uppermost and stretched across the larval 

 chamber where it fits very tightly, suggests the explanation that this is 

 a contrivance for avoiding or preventing the attacks of parasites or other 

 predaceous enemies during the prolonged hibernating period. This 

 suggestion is made by Connold and is, I think, a very probable one. 

 He, however, states that pupation takes place in October. Of course, 

 this may be so in the South of England, although I doubt it. 



The larvae of U . cardui remain head downwards during the winter 

 (Mik), and Gourcau notes that the larvae of U. cuspidata also remain 

 in this position until pupation commences. In Dufour's account of 

 the life-history of U. quadrifasciata there is no mention of this peculiarity ; 

 it may be inferred, however, that the larvae of this species hibernate 

 in a similar manner to those described. 



I have never been able to convince myself that frass is present in 

 the larval chambers. In tlie galls of Cirsium arvense caused by larvae 

 of U . cardui, Mik found in the upper portions of the larval chambers 

 " Excreraenten in der Form von lichtbraunen Kriimchen " ; possibly 



