644 THE MICROSCOPE 



they have a mouth adapted for biting such food, and are 

 covered with a hard and very brittle skin. The Bdellidce 

 live among damp moss, have the body divided apparently 

 into two parts by a constriction, and the rostrum and 

 palpi very long ; whilst Trombidiidce, of which the little 

 scarlet mite so often seen in gardens is an example, have 

 their palpi converted into little raptorial organs. 



Another family of parasites are commonly met with in 

 the bodies of fishes, attaching themselves to the branchiae, 

 to the soft skin under the fins, or to the eyes, much to 

 the annoyance of the unfortunate victim. Some of these 

 found on fresh-water fish are sufficiently transparent to 

 show the circulation of their fluids most interesting 

 objects for the microscope. 



The "Water-snail, Limnoeus^ is tormented by a larva of 

 the family Amphistoma, which attaches itself by a series 

 of hooklets and bristles to various parts of the body and 

 mantle ; under a low magnifying power, when congre- 

 gated together, they appear somewhat like tufts of threads. 1 



ARACHNIDA, Spiders. Epeira diadema is the best 

 known of the British species of Garden Spiders: it 

 is readily recognised by the beautiful little gem-like 

 marks' on its body and legs. Spiders abound on every 

 shrub ; and if we consider that the Spider is destitute of 

 a distinct head, without antennae, one-half of its body 

 attached to the other by a very slender connexion, and so 

 soft as not to bear the least pressure, -its limbs so slightly 

 attached to its body that they fall off at a very slight 

 touch, it appears ill-adapted either to escape the many 

 dangers which threaten it on all sides or to supply itself 

 with food ; and the economy of such an animal is deserving 

 of the microsccpist's attention. 



The several important organs peculiar to the Spider 

 tribe are represented in fig. 299. Of these, No. 1 show 

 the spinning apparatus; four only are the spinnarets, or 

 organs by which their silky threads are emitted. Their 

 structure is very remarkable ; the surface of each spinnaret 

 is pierced by an infinite number of minute holes, shown 



(1) The earliest known account of the parasite tribes is given in Redi's 

 Treatise de Generations -Insectorum ; see also H. Denny's Monographia 

 rorum Britannia. 1842. 



