1884.] Agricultural Botany. 573 
cause luminosity (Fig. 4). It may be pertinent to cite Quatrefages’ 
description of the luminosity of some ' 
marine animals.! I have observed that 
the light flashes in jets along the so- 
mites of these worms as if the seg- 
mental organs had something to do 
with its production and with the func- 
tion of respiration. I have also shown 
that in the housefly the air-cells in 
the proboscis expand at each act of 
driven into the tracheal end-cells, Fic. 4.—Stellate terminals (S) 
as into the chambers of our own Of trachea F, luminous lat cells. 
| : : After Schultze. 
ungs, and that in this way the 
Ussues are directly aérated. The slower process of aération by 
the intervention of the blood may suffice in some larve, as in 
Crustacea, but the chief function of the blood of insects seems to 
be the conduction of food from the intestinal walls to the various 
s, 
To sum up. The tracheæ of insects and similar organs are 
“upported by chitinous fibers which are crenulations accompanied 
by thickening of the chitinous intima with which they remain 
Sentinuous ; their dorsal fissure and flexibility providing for the 
) enlargement and reduction of the cavity; and the oxygenation of 
Cg has its seat chiefly at the extremity of the tracheal 
Mes es, and not by diffusion from the tracheal trunks into the 
x @ he 
AGRICULTURAL BOTANY. 
BY E, LEWIS STURTEVANT, M.D. 
: TH Secret of classification consists in the understanding of 
Motive, of which form and structure are exponents. The 
motive of plants is to secure existence and perpetuation, 
‘atural 
is And parts and habits are and have been so formulated as to com- 
Pass this 
kiai object as against difficulties of very varied character. 
idual plant is in a state of unstable equilibrium, ever 
i 
Ann. d. Se; Ne 
i + Nat., Vol, xix (1 
: Pyche, No. 100 (Aug., 882). 
