516 THE MICROSCOPE. 



which a little resin had been dissolved previously : prepared 

 in this way, they retain their forms and keep well for years. 

 Swammerdam discovered that the fatty material in insects 

 is perfectly soluble in spirit of turpentine ; after steeping 

 in it, he washed them well out with water, and was thus 

 enabled to show the viscera plainly. He frequently spent 

 whole days in cleansing a single caterpillar, in order to 

 trace the structure of its heart. His singular mode of 

 stripping off the skin of the caterpillar, just as it is on the 

 point of spinning its cone, was effected by taking hold of 

 its thread, and letting it drop into scalding water, then 

 suddenly withdrawing it. After this it was immersed in dis- 

 tilled vinegar and spirits of wine mixed in equal propor- 

 tions, which gives firmness to the whole, and the exuvia 

 or skin readily separates : the pupa is sometimes seen 

 enclosed, and the butterfly in the pupa. 



The following list comprises a few of the insects, whose 

 eyes, antennae, &c., are best adapted for microscopic prepa- 

 rations : Coleoptera Cincindela,Dyticm, Melolontha,Luca- 

 nus, Stag-beetle, D iamond- beetle ; Orthoptera Acheta, 

 Crickets, Locusta, (fee. ; Hemiptera Notonecta, Boat-fly ; 

 Neuroptera Libellula, Agrion; Hymenoptera Vespidae, 

 Apidce, Wasps and Bees of all kinds ; Lepidoptera 

 Vanessa, and all the various species of Butterflies, Sphynx, 

 or Privet Hawk-moth, Bombyx, Silkworm-moth, &c. ; 

 Diptera Tabanm, Gadfly, Eristalis, Drone-fly, Titpula, 

 Crane-fly, Musca, House-fly, &c. 



The circulation of the blood can be watched in many 

 of the larvae of insects ; that in the larva of the Ephemera 

 marginata, Day-fly, is very interesting, being a series of 

 small currents diverging from the gill-like appendages 

 placed near the head. In the larva of the Gnat, the body 

 is almost entirely occupied by the visceral cavity ; and the 

 blood is seen to move backwards and forwards in the 

 space that surrounds the alimentary canal, which here 

 serves the purpose of the channels usually running through 

 the solid tissues. This condition very nearly approximates 

 to that found in many Annelida. 



In the wings of pupse of many insects, the circula- 

 tion may be seen ; in that of the Agrion puella, a small 

 Dragon-fly, each of the " nerves " of the wings contain 



