84 JOURNAL OF THE [January 



90,000 lines per inch was the most I could resolve. Mr. Fa- 

 soldt says the 110,000 band is the highest one he knows to have 

 been resolved by the same tV objective by transmitted light. It 

 would be very interesting to know what kind of rulings Prof. 

 Abbe used in determining the theoretical resolving power of an 

 objective, as well as the method of illumination. 



AN ICHNEUMON-FLY, MICROGASTER, PARASITIC 

 ON THE LARVA OF A HAWK-MOTH. 



BY F, W. LEGGETT. 

 {Read October "jth, 1887.) 



This parasite lays its eggs within the body of the larva of the 

 Hawk-Moth. For this purpose it pierces the softer parts of the 

 body with its ovipositor, but carefully avoids vital spots. 



When the egg is hatched, the grub eats the body of the larva 

 until fully fed, makes a hole through its skin, and, emerging, 

 commences spinning a beautiful white cocoon, attaching this 

 carefully to the still-living body of its late home. 



This cocoon is provided with a very perfectly-fitting door, 

 which, when the imago is ready, he opens, and a full-fledged 

 Ichneumon-fly appears, winged for flight. All cocoons, how- 

 ever, do not have the door attachment. When this is ab- 

 sent the imago bites a hole through the cocoon with its man- 

 dibles. 



It is remarkable how completely these parasites consume the 

 larva, and how long the larva retains life. When it dies it col- 

 lapses, and its skin can be inflated like a bladder. 



If I am not in error, these parasites are infested with para- 

 sites, which can be seen, both in the larva and imago, under the 

 microscopes. 



Under one microscope is the larva of an Ichneumon-fly fully 

 fed, taken as it emerged from the body of the larva of a Moth. 

 Under the other microscope are some cocoons with the imago 

 emerging, and also free. In a bottle is a Hawk-Moth larva with 

 Ichneumon cocoons attached. The glass-covered box contains 

 some cocoons, and a number of Ichneumon-flies, living and 

 dead. It will be observed that these cocoons do not have 

 doors, or covers. 



