210 MR. A. M. ALTSON ON THE LIFE-HISTORY AND 



that the sense-orgMns iu the antenna} and the palps of the 

 ovipositor had suddenly received the odour of the carrion and 

 stimulated the insect to oviposit. The males are also attracted 

 by cairion — apparently a, sexual tropisni to enable them to locate 

 the females. Marshall (3) observes: — " They " (both sexes) " scent 

 the aroma, of carrion at a surprising distance, as I once had 

 occasion to observe in watching the remains of a dead rook, upon 

 which they descended in constant succession, apparently from the 

 sky, like vultures. The males generally alighted on blades of 

 grass close to the attractive object, as if to Avait for their 

 partners, without inteiiupting them in their unsavoury occu- 

 pation." 



As soon as the feniales have alighted, they begin theii* search 

 for the laTvee, and if the initial effort to insert the ovipositor is 

 successful, they remain depositing eggs until they die, either from 

 exhaustion or because their task is completed. A few have been 

 observed to leave the larvpe and go in search of food and not 

 return the same day. 



Only one egg is deposited in each larva by an individual 

 female, at least, under conditions which are approximately 

 natural — i. e., where the larva has means of escape by disappearing 

 into the meat or earth. 



The ovipositor is inserted diagonally under the integument of 

 the larva when the attack ta,kes place in the thoracic or 

 abdominal regions. The larva makes every effort to escape, 

 wriggling and squirming, and frequently damaging the female. 

 These frantic efforts to escape are put an end to by the effect of a 

 poison injected with the insertion of the ovipositor. The 

 immediate effect of the insertion of the ovipositor is to cause the 

 larva to vomit and void. The poison produces a paralyzing 

 effect, and causes the larva to contract and then lie motionless 

 whilst the egg is deposited. This operation varies in time, and 

 may take 30 seconds to 5 minutes* — the more exhausted the 

 female is, the longer it takes. 



The "temporary paralysis" of the larva lasts from one to two 

 minutes, so that when an exhausted femaJe delays the with- 

 draAval of the ovipositor the larva endeoavours to release itself; 

 normally though, when the ovipositor is withdrawn, it is still 

 motionless, and remaiiis so for some seconds. The femaJe then 

 moves off in search of another victim. , The first movements of 

 a larva recovering from the " tempoiary paralysis" are to extend 

 itself to its full lengtli, and then, still slightly under the influence 

 of the poison and the unpleasant ovipositor, it goes through a 

 series of extraordinary convulsive and constrictive movements, 

 which ripple the integument either from the cephalic to the 

 anal end or vice versa, as though it was endowed with intelligence 



* One female, which had uot oviposited in more than a dozen larvEe, was observed 

 to retain the ovipositor within a larva for 21 minutes, and as the initial dose of 

 poison did not sutfice to keep it motionless, further doses were apparently' 

 administered each time it moved. Needless to say, this larva died. 



