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OVIPOSITION IN THE CELERY ELY. 

 By T. H. TAYLOR. 



(Willi one Text-figure.) 



The habits of tlie Celery Fly are comparatively easy to study, for, 

 besides beiii<T conspicuously coloured and of fairly larf^e size, the flies 

 are obliging enough to proceed with their occupations when the observer 

 approaches, gaily sporting their dappled wings and seeming but little 

 embarrassed by his presence. A sunny afternoon is a favourable time 

 for watching the flies lay their eggs, and although the details of the 

 process are too minute to be seen from a distance, its general features 

 can be followed without much trouble. After sunning itself on the 

 upper surface of a leaf, a fly about to lay, crawls over the edge to the 

 underside of the leaf, and, testing the surface with its tongue, proceeds 

 to drive the tip of the ovipositor into the interior of the leaf. In a few 

 seconds, the boring action ceases and is shortly followed by more genera- 

 lised movements of the body such as in an insect are commonly as- 

 sociated with the process of egg-laying, and whose purpose is clearly to 

 disengage an egg and pass it to the outside. Visiting other and often 

 adjacent parts of the leaf, the insect lays two or three eggs one after 

 another in quick succession, and then without displaying any further 

 interest in the results of its labour flies off to fresh ground. If the leaf 

 be now plucked and the lower surface examined with a lens, the 

 punctures made by the ovipositor can be seen and also the eggs them- 

 selves each lying beneath the cuticle in a separate space in the paren- 

 chyma. 



By imprisoning a fly in a glass tube or capsule and giving it a piece 

 of celery leaf, one can watch the process of egj^laying under the micro- 

 scope. After the pointed end of the ovipositor has pierced the epidermis, 

 the body of the tube, two-edged and file-like, forming an efficient boring 

 apparatus, passes into the tissue beneath and breaking down the cells 

 around it prepares a cavity for the reception of the egg. Having cleared 

 a suitable space, the fiy charges the tube which, still extended into the 

 leaf, has become for the moment relaxed and inert, and then, with a final 

 efl"ort expels the egg through the terminal opening and crawls away. The 

 process from the insertion of the tube to its withdrawal lasts from about 



