CHAPTER XIX. 



Tab. XXXIII. 



Fig. 1. The organs for forming the silk consist of two long vessels. 

 They unite to form the spinneret (fusulus) through which the larva 

 draws the silken thread eraploj'-ed in fabricating its cocoon, a, a, the 

 silk bags, b, the spinneret. 



Fig. 2, The web of spiders is also a kind of silk, remarkable for its 

 lightness and tenuity ; it is spun from four or six anal spinnerets, the 

 fluid matter forming the web being secreted in adjacent vessels, a, b, 

 c, d, the spinnerets. 



Fig. 3. Panorpa communis, (Linn.) is an insect frequently seen in 

 meadows during the early part of summer. It is a long-bodied fly, of 

 moderate size, with four transparent wings, elegantly variegated with 

 deep brown spots. 



Fig. 4. The female glow-worm. 

 Fig. 5. The male of the same insect. 



Fig. 6. The larva of some dragon-flies {ashna and libellula, F.) 

 swim by strongly ejecting water from the anus. By first taking in the 

 \vater, and then "expelling it, they are enabled to swim. This may be 

 seen by putting one of these larva into a plate with water. We find 

 that while the animal moves forward, a current of water is produced 

 by this pumping in a contrary direction. Sometimes it will raise its 

 tail out of the water, when a stream of water issues from it. 



Fig. 7. The spiracula, or breathing pores of insects, are small ori- 

 fices in the trunk or abdomen, opening into a canal called the trachecB ; 

 by which the air enters the body, or is expelled from it. In the larvae 

 or caterpillars, a trachea runs on each side of the body, under the 

 skin, and generally opens externally by nine or ten apertures or spira- 

 culffi ; from these the same number of air-vessels of a silver colour 

 pass off to be dispersed through the body, a, a, spiracula ; b, b, tra- 

 chea. 



Fig. 8. The pupse of gnats suspend themselves on the surface of 

 the water, by two auriform respiratory organs on the anterior part of 

 the trunk, their abdomen being then folded under the breast ; when 

 disposed to descend, the animal unfolds it, and with sudden strokes 

 which she gives with it and her anal swimmers to the water, she swims 

 from right to left, as well as upwards and downwards, with the great- 

 est ease. 



FjG. 9. This is a well known fly, (stratyonis chamcdeon, F.) chame- 

 leon fly. In its first state it inhabits the water, and often remains 

 supported by its radiated tail, consisting of beautiful feathered hairs or 

 plumes, on the surface, with its head downwards. But when it 

 is disposed to seek the bottom or to descend, the radii of the tail is 

 formed into a concavity including in it an air bubble ; this is its swim 

 bladder, and by the bending of its body from right to left, contracting 

 itself into the form of the letter S, and then extending itself again in- 

 to a straight line, it moves itself in any direction. 



