PLATE 1 
Fig. A.—Portion of the large longitudinal trachea of the house fly cut crosswise 
obliquely, showing the carmine acid “precipitate '* pr. X190. The fly had been 
submerged for one hour in a pure nicotine solution (1 : 500) colored with carmine 
acid. 
Fig. B.—Combination drawing from two consecutive sections of a green peach 
aphis, showing the indigo-carmine " precipitate ** pr in a trachea ir. X500. The 
aphis had been submerged for 45 minutes in a pure nicotine solution (1 : 500) col¬ 
ored with indigo-carmine. 
Fig. C.—Cross section of a large longitudinal trachea of larva of lesser wax moth, 
showing the indigo-carmine “precipitate” pr adhering to the tracheal wall trw. 
X190. The larva had been submerged for 30 minutes in a pure nicotine solution 
(1:500) colored with indigo-carmine. 
Fig. D,—Longitudinal section of one of the smallest tracheae of the same larva 
as in figure C; same treatment and same enlargement. 
Fig. E.—Longitudinal section of a large trachea and one of its branches of a coccid, 
showing the ' ‘ precipitate ” pr resulting from the union of pure nicotine and phospho- 
molybdic acid. X500. The coccid had been submerged for 30 minutes in a pure 
nicotine solution (1 :100). 
Fig. F.—Portion of a cross section of an aphid ( Aphis rumicis), showing the indigo- 
carmine “precipitate” pr in a spiracle sp. X320. The aphid had been heavily 
sprayed with a pure nicotine solution (1 : 500) colored with indigo-carmine. 
Fig. G.—Portion of a cross section of the same aphid as in figure F, showing no 
precipitate in the trachea tr, but much on the outside of the integument int. X 320. 
Fig. H-O.—Longitudinal sections of spiracles sp with connecting tracheae tr , 
showing how it is practically impossible for aqueous spray solutions to enter spiracles, 
owing to hairs hr, a closing plate p, and a peculiar arrangement of rims r at mouths 
of spiracles. 
Fig. H. —Spiracle of a coccid ( Orthezia insignis). X 500. 
Fig. I.—Spiracle of a caterpillar of Atteva aurea. X 190. 
Fig. J.—Spiracle of a larva of lesser wax moth ( Achroia grisella). X 190. 
Fig. K.—Spiracle of a caterpillar of Datana sp. X 500. 
Fig. L.—Spiracle of a caterpillar of a catalpa sphinx ( Ceratomia catalpae.) 
X 500. 
Fig. M.—Spiracle of a larva of a Colorado potato beetle (Leptinoiarsa 
decemlineata). X 500. 
Fig. N.—Spiracle of fall webworm (caterpillar of Hyphantria cunea). X 320. 
Fig. O.—Spiracle of the tomato worm (larva of Phlegethontius sexta ), show¬ 
ing the closing plate p. X 50. 
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