Observations on the Turnip Saic-Fly. 



373 



consistence^ but become a white powder when dry. Like many 

 other animals, they repose after the heat and fatigues of the day, 

 and generally rest beneath the leaves or in the flowers, with their 

 heads and bodies bent down, and their antennae lying close, until 

 the rays of the morning sun awaken them to their toils. 



The saw-flies generally appear in May, sometimes earlier, 

 "when the males fecundate the eggs in a few seconds, but this 

 only takes place in the hottest sunshine, whilst the female rests 

 upon a leaf, as is the case with the white cabbage-butterfly ; after 

 which she immediately begins to deposit her eggs : she first ex- 

 amines a leaf with the point of her ovipositor, and then, fixing 

 herself upon the edge, with her legs equally placed on both sides, 

 holding particularly fast with the hinder, for which purpose the 

 suckers are admirably adapted, she thrusts her saws into the mar- 

 gm, makes a shallow slit, and insinuates the instruments (figs. 1 7 

 and 18) obliquely, sometim.es nearly parallel, into the edge of the 

 leaf backward : having forced them in nearly to the base, she brings 

 them round, forming the segment of a circle, and thus separating 

 the cuticles she forms a ca\ity with her saws or lancets, which 

 may be readily seen with the aid of a lens, by holding the leaf up 

 to the light. The cutting this cavity often occupies half a mi- 

 nute, when the oval, whitish, and semitransparent egg passes 

 through the united lancets, which form a tube to conduct it to its 

 nidus ; the fly, at the same time, injecting a small portion of fluid,'^ 

 which keeps the eggs moist, and prevents the cuticles from wi- 

 thering and collapsing upon, or exposing it to sudden changes 

 of temperature and other casualties. The four lancets are then 

 leisurely vrithdrawn and returned to the abdomen until the ope- 

 ration is repeated, and five or six eggs (fixgs. 1:, 1) are thus laid, in 

 distinct cells, in about twenty minutes, j Such are the care and 

 instinct manifested by the female, that, if she commence to 

 penetrate a leaf where there is not room, or if there be any dan- 

 ger from the leaf being curled, or too near an egg already depo- 

 sited, she relinquishes her object until she finds a more suitable 

 spot ; and she has never but once been detected lading her eggs 

 in the seed-leaves, so provident is she of the future wants of her 

 progeny, well knowing such leaves would possibly be withered 

 before the eggs hatched. Mr. Marshall placed a female upon a 

 succulent leaf of the rape (Bfassica Kapus), but she refused to 

 deposit any eggs, although she did so immediately on being put 

 upon a young turnip-leaf; this she effected twice, and afterwards 

 laid an egg on the margin of a large hole eaten in the leaf, which 

 is attended with greater difiiculty than in her more usual way on 



* Vide Mr. Newport's valuable Essay. 



f We were first indebted to Mr. Marshall for these careful details, which 

 have been verified by Mr. Milburn and Mr. Newport. 



