DKVELOPMENT OF GALLS OF CECIDOMYIA ULMARI^. 



13 



About the 30th of October, 1877, when these galls were 

 exceedingly plentiful by one of the streams in the neighbour- 

 hood of Isleworth, my attention was attracted by the great 

 variety of shape on the part of the gall-growths beneath the 

 leaves, some (apparently still in their earliest stages) being 

 simply like a white blister, or semi-globose protuberance, 



Development of galls showing — 1. First stage. 2. Further development, 

 with funnel-shaped extremity. 3. Fully developed gall. 4. The same, in 

 section. 5. Gall spread oiien after exit of the larva. 



beset with white silky hairs (fig. 1) ; others globose and 

 prolonged to a funnel-shaped extremity (fig. 2) ; whilst other 

 fully-grown specimens had the funnel-shaped extremity 

 broader and more developed, or open for the exit of the 

 gall- gnat larva. 



On carefully examining the gall in its first stage by 

 pressing the side of a fine needle across the convex top, it 

 would be found there was a narrow strap-like process (the 

 future funnel-shaped extremity) folded flatly down on it, in 

 the same way as the tip of a glove can be laid on the 

 contained finger. As growth proceeded this folded extremity 

 altered its position to the complete funnel-shape given at 

 fig. 2, the long blunt point being divided into two parts by a 

 slit on each side, running about a third of the length of the 

 gall and gradually widening, till at the time for the evolution 

 o( the larva the outer husk of the gall was merely a globose 

 case, tubular below, of two somewhat leaf-like portions of 

 filmy tissue, closely applied by their edges and guarding the 

 true gall, uiuch as the young filbert is guarded in the long 

 projecting husk, and varying from the portion exposed on 

 the upper side of the leaf in being usually while, and thickly 

 beset with white hairs. 



The inner or true gall is similarly globose, and somewhat 

 pointed, usually single-celled, of thin tissue, more succulent 

 towards its base, and white ; flocculenl outside, but of perfect 



