HABITS OF TWO PARASITES OF BLOW-FLIES. 225 



fly-nymph, neither one containing a fully-foi'med fly which for 

 some reason has died or failed to emerge, nor will it oviposit in 

 an empty pnparium from which the occupant or occupants have 

 emerged, although eflbrts to induce some to do so were made by 

 burying that portion from which emergence took place ; its 

 behaviour with such puparia is initially the same as with a 

 healthy puparium, but after examination and possibly an attempt 

 to insert the ovipositor, it cra.wls off" in search of others. To 

 enable it to distinguish between those pupaiia which contain 

 sustenance for its progeny and those which do not, the female 

 must not only possess very delicate sense-organs, but apparently 

 uses the point of the ovipositor, as will be shown later. 



Before attempting to insert the ovipositor, a female spends 

 some time critically examining the puparium, crawding over and 

 around it, with her head inclined towards it, constantly waving 

 the antennae, with which she frequently touches it. Having, 

 apparently, satisfied herself that it is a fit object for attack, she 

 bends the abdomen so that the apex touches the puparium, and 

 then with the tactile hairs upon the palpi and abdomen, and with 

 the point of the ovipositor, she pi'oceeds to prod it until a position 

 is located — such as a groove in the contracted integument of the 

 puparium — through which to make a puncture. The ovipositor 

 is then held in the minute groove, and the apex of the abdomen 

 springs back to a position in which it assumes almost its natural 

 shape, although diagonally opposed to the puparium, and in doing 

 this the full length of the ovipositor is exposed (text-fig. 18) ; 



Text-figure 18. 



Female JV. &reuicor»/s ovipositing; 1st position. Greatly- magnified. 

 Original. 



this has hitherto been hidden in its recess along the ventral plates 

 of the abdomen. The female now endeavours to pierce the 

 puparium — not always with success, in which case she moves ofl:' 

 to another spot and repeats the process, — which she appears to do 

 with a slight rotatory and up-and-down movement of the ovi- 

 positor, accompanied with frequent twitching of the antennae, a 

 constant movement of the trophi, a slight twitching of the apex 

 of the abdomen, and a general appearance of slight movements as 

 if her entire strength was being exerted upon the task. As the 

 ovipositor gi-adually disappears into the puparium, the position of 



