INSECTS. 515 



The female Flea, fig. 268, lays a great number of eggs, 

 sticking them together with a glutinous matter; the Flea 

 infesting the dog, or cat, glues its eggs fast to the roots of 

 the hairs; in four days' time the eggs are hatched, and a 

 small white worm or grub is seen crawling about, and 

 feeding most actively. No. 4, fig. 221, is a magnified view 

 of one, covered with short hairs, doubtless for the pur- 

 pose of preventing its dislodgment. After remaining in 

 this state about nine or ten days, it assumes the pupa form, 

 which it retains four days ; and in nine days more it becomes 

 a perfect Flea. The head of the Flea found in the cat 

 (No. 3, fig. 221) is seen to be somewhat different in form 

 from that of the Flea infesting the human being. Its 

 jaws are furnished with formidable booklets, and from the 

 first and second joints behind the head short strong spines 

 project; these are for assisting it in maintaining a firmer 

 and better hold on the animal. 



We have before referred to S warn mer dam's careful dis- 

 sections under the microscope. In no department of 

 nature did he bestow so much care, as in this of the 

 insect tribes. He first killed them by immersion in 

 spirits of wine and water, or in spirits of turpentine ; pre- 

 serving them for some time in the same fluid, to give 

 firmness, and render dissection more easy. 1 When he had 

 divided the insect transversely with fine scissors, he par- 

 ticularly noted the relative position of the various parts, 

 and then proceeded to remove the viscera very cautiously 

 with fine -pointed instruments, carefully washing away all 

 the fat and other matters with soft camels'-hair pencils ; 

 by putting the whole into water, and then shaking them 

 gently, he separated the air-vessels, or tracheae, in a 

 perfect state from the other parts. At other times, he 

 made use of a very fine syringe, to inject water into and 

 thoroughly cleanse them ; after which they were distended 

 by blowing in air, and hung up to dry. Sometimes he 

 succeeded better by first immersing the insects in liquid 

 balsam ; again, he frequently made punctures with a fine 

 needle, and after squeezing out the soft parts through the 

 holes made in this manner, he blew air into their interiors 

 by means of a very slender glass tube, then having dried 

 them in the shade, anointed them with oil of spike, in 



(1) The vapour of cyanide of potassium, in a close-stopped wide-mouthed 

 bottle, kills all insects without injury to their appearance in any way. 

 LL 2 



