PREPARATION OF INSECTS. 337 



Another family of parasites are commonly met with in the bodies 

 of fishes, attaching themselves to the branchia, to the soft skin under 

 the fins, or to the ej'es, much to the annoyance of the unfortunate vic- 

 tim. Some of those found on fresh-water fish are sufficiently transparent 

 to show the circulation of their fluids — a most interesting sight. 



The water-snail, Limneus, is infested with a parasite of the family 

 Clepsinida, which attaches itself by a series of booklets and bristles to 

 such parts of the body and mantle as give a secure lodgment to it ; 

 they look like little tufts of thread hanging from the sides of the ani- 

 mal, without its having the power to dislodge them.* 



We have before referred to Swammerdam's careful dissections 

 under the microscope. In no department of nature did he bestow more 

 care than in his many examinations of insects. He first killed them 

 by immersion in spirits of wine and water, or in spirits of turpentine ; 

 preserving them for some time in the same fluid, to give firmness, and 

 render his dissections more easy. When he had divided the insect 

 transversely with his fine scissors, he particularly 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 fine camels'-hair pencils ; or, by 

 putting the whole into water and then shaking them gently, he se- 

 parated the air-vessels, or trachsea, 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. He is said to have often suc- 

 ceeded by immersing, insects in balsam. Again, he frequently made 

 punctures in some insects with a fine needle, and after squeezing out 

 all their moisture through the holea made in this manner, he filled 

 them with air by means of very slender glass tubes, then dried them in 

 the shade, and afterwards anointed them with oil of spike in which a 

 little resin had been dissolved : those prepared in this way retained 

 their forms and kept well for years. Swammerdam discovered that 

 the fat of all insects was perfectly soluble in spirit of turpentine ; after 

 steeping them in it, he washed them well in water, and was thus en- 

 abled to show the viscera plainly. He frequently spent whole days in 

 thus cleansing a singl* caterpillar of its fat, in order to discover the 

 structure of its heart. His singular mode of stripping off the skin 

 of the caterpillar, just as it was on the point of spinning its cone, was 



*■ A veiy interesting accotmt of the parasite tribes is given in Rhedi's Treatise de 

 Generatione Insedorum, and in B.Denny'B Monographia Anopliirorum Britanniw, 

 Bohn, London, 18i2. 



