Fig. 39.—VIEW OF THE BLOOD-VESSELS AND OTHER PARTS IN A PORTION OF THE UPPER 
SURFACE OF THE TONGUE OF A FROG, THE REAL MAGNITUDE OF THE SURFACE 
DELINEATED BEING A CIRCLE THE 120TH OF AN INCH IN DIAMETER. DAGUERREO- 
TYPED BY MESSRS. DONNlS AND FOUCAULT. 
MICROSCOPIC DRAWING & ENGRAVING. 
CHAPTER II. / , 
25. Natural tests not invariable.— 26. Natural tests imperfect standards. 
—27. Nobert’s test-plates.— 28. The degree of closeness of their lines. 
—29. Their use.— 30. Apparent error respecting them.'— 31. Fro- 
ment’s microscopic engraving.— 32. Method of executing it.— 33. 
Various methods of microscopic.drawing.— 34. Drawings by squares. 
—35. .Dr. Groring’s drawings.— 36. Structure and metamorphosis of 
insects.— 37. The day-fly.— 38. The larva of this insect.— 39. Its 
organs of respiration.— 40. Its general structure.— 41. Its mobility.— 
42. State of chrysalis.— 43. The perfect insect.— 44. The production 
and deposition of its eggs, and its death.— 45. Death may be delayed 
by postponing the laying of the eggs.— 46. They take no food.— 47. 
Their countless numbers ; their bodies used as manure. 
Lardner’s Museum op Science. f 
No. 69. 
65 
