PLATE 3 
Fig. A to I, L, M.—Drawings and diagrams representing the distribution of pre¬ 
cipitate resulting from the fumes of 40 per cent nicotine sulphate and phosphomolybdic 
acid. Figures A, B, F to I are from the same green peach aphis, and figures L and M 
are from the same house fly that had been fumigated. X 320. Figures Dand E are 
diagrams, after Baker (2), representing the respiratory system of an aphid, Eriosoma 
lanigerum. 
Fig. A.—Transverse-longitudinal section of a trachea of an aphid, showing the 
precipitate pr inside the trachea and in fat cells fc near by. 
Fig. B.—Cross section of a portion of an aphid just molting, showing the 
precipitate pr on the outer surfaces of the old int x and the new integuments int 
and between them, but none in the fat cells fc. 
Fig. C.—Combination drawing from six consecutive sections through thoracic 
ganglion of an aphid, showing the precipitate pr in three tracheal branches tr 
in the cortical layer cl and in the inner layer il of a ganglion. 
Fig. D.—Diagram of the dorsal tracheal system of an aphid, showing the 
dorsal trunk dt and dorsal arch da. 
Fig. E. —Diagram of the ventral tracheal system of an aphid, showing the 
anterior ventral arch ava, posterior ventral arch pva, and the ventral trunk vt. 
Fig. F.—Combination drawing from five consecutive sections through the 
thorax of an aphid, showing the precipitate pr on the outer surface of the 
integument int, in the tracheae tr and in the subesophageal ganglion sg. 
Fig. G.—Portion of cross section of an optic lobe of an aphid, showing the 
precipitate pr inside and outside a tracheal branch tr. 
Fig. H.—Cross section of the brain br and optic lobes opl of an aphid, showing 
the precipitate pr in the tracheal branch tr and in the cortical’ layer of the 
brain. 
Fig. I.—Cross section of two ovaries ov of an aphid, showing the tracheal 
branch tr containing precipitate passing between them. 
Fig. L.—Cross section of two trachese tr and a fat cell/c of a house fly, showing 
the precipitate pr in the tracheae and in the fat cell outside its nucleus. 
Fig. M.—Longitudinal section through a spiracle sp and its connecting 
trachea tr of a house fly, showing the precipitate pr in the neck of the spiracle 
and along the tracheal wall. 
Fig. J and K.—Cross sections of the small tracheae, showing the precipitate pr in 
newly formed tracheal walls trw resulting from the union of pure nicotine and phospho¬ 
molybdic acid. These and other insects had been submerged in pure nicotine for 35 
minutes. X 190. Figure J is from a house-fly larva and figure K from a lesser wax- 
moth larva. 
Fig. N and Q .—Cross sections, showing how well Camoy’s fluid passes through 
hard cliitin, as indicated by remaining crystals pr of mercuric chlorid. Figure N is a 
trachea from a lesser wax-moth larva. X 190. Figure Q shows a portion of the 
integument int and the fat cells fc of an aphid, also showing the physical change in the 
fat cells caused by a fixative. X 500. 
Fig. O.—Cross section of a medium-sized trachea of a lesser wax-moth larva, showing 
that pure nicotine did not pass into an older tracheal wall trw under the same condi¬ 
tions as stated for figure K. X 190. 
Fig. P.—Cross section of portion of the integument int of an aphid ( Aphis rumicis), 
showing that pure nicotine did not pass into chitin under same conditions as stated for 
figures J, K, and O. X 500. 
