XVlll 



President's Address. [Aug. 28, 



Ichneumons, But whereas noses, either long or short, do not imply a 

 greater or lesser keenness of scent, we can from the length of the 

 insect's ovipositor judge what kind of prey she will select for her 



progeny. 



Let us choose this one with an ovipositor nearly two-thirds of an 

 inch long and follow her. She is agile, supple, with legs made for 

 running ; the antennae or feelers are constantly vibrating ; she walks 

 by jerks, her wings are slightly moving and half expanded. What is 

 she looking for ? why this continual vibration of the ante,mce, these 

 half-expanded wings ? Is she listening to a sound audible only to 

 herself ? The most skilful physiologist has not been able, as yet, to 

 find a special auditory vesicle (with otoliths) in an insect, and yet that 

 power exists. 



Can it be that the expanded wings act as an auricular drum, and the 

 antennae as an olfactory organ ? It may be so, but we have to be very 

 careful in building theories. While I am indulging in these con- 

 jectures I have lost sight of the insect. Has she flown ? Where is 

 she ? I look at the other side of the bough. There she is ; but what 

 is she doing ? She stands firmly fixed, her front legs apart, her head 

 on the bark, her long pedunculated abdomen raised high, and the 

 ovipositor at a right angle with the body. What a curious position ! 

 Can it be that the insect is also affected by the stupendous heat of the 

 sun, which sends large beads of perspiration coursing down my cheeks ? 

 Now she changes her place, goes a few inches further, comes back, 

 the vibration of the antennae ceases, the same position is again assumed, 

 .and, behold, the ovipositor disappears, with difficulty evidently ; the 

 two blades of the sheath are open at the tip, little by little all is 

 inserted ; with a brusque effort it is extracted again, and the 

 Ichneumon, after brushing her antennce with her fore legs, is off ■ before 

 I have time to bring my net in action. Where did she insert that long 

 ovipositor ? 1 cannot find an aperture, and yet there must be one. 

 My knife is soon at work on the half -rotten bough. I tear away with 

 great caution, Alas ! for the caution. My last cut brings to light a 

 small gallery, and within a grub which my knife has badly damaged. 

 Mutilated as it is, I very soon conclude that it is the larva of a weevil. 

 With the help of my magnifying glass I soon observe some slight 

 puncture, most minute spots on some of the segments, and when I 

 dissect it at home' I find some eggs under the epidermis. 



I shall now by analogy reconstruct the sequel of the evolution of 

 the parasitic egg, and of the weevil which my knife has so soon sent 

 to limbo. The eggs are soon hatched, and the grub will begin either 

 sucking or gnawing all the non-vital parts of the host, and, only when 

 it feels that its time has come will it perforate the outer teguments 

 and spin a cocoon, generally, but not always, adhering to the skin. It 



