Economic entomology for the farmer and the fruit grower, and for use as a text-book in agricultural schools and colleges; economicentomolo00smit Year: 1906 32 AN ECONOMIC ENTOMOLOGY. of enormous distention compared with the size of the insect, and this is to accommodate the honey collected by the insects to be carried into the hive. In the use of poisons acting through the stomach, the arsenic, which is usually employed, is taken in with the food and gener- ally carried into the chylific ventricle before it becomes effective. In the crop the food is generally too dry to cause the necessary s
Economic entomology for the farmer and the fruit grower, and for use as a text-book in agricultural schools and colleges; economicentomolo00smit Year: 1906 32 AN ECONOMIC ENTOMOLOGY. of enormous distention compared with the size of the insect, and this is to accommodate the honey collected by the insects to be carried into the hive. In the use of poisons acting through the stomach, the arsenic, which is usually employed, is taken in with the food and gener- ally carried into the chylific ventricle before it becomes effective. In the crop the food is generally too dry to cause the necessary solution of the caustic properties of the arsenic, which is neces- sarily applied in its least soluble form ; but by the time it has passed through the gizzard and has reached the stomach, becom- ing moistened and mixed with the secretions that have been already mentioned, it becomes active. Some insects are able to take a very large quantity of poisonous material without injury ; succumbing only after two or three days to the effects of a poi- sonous meal. It is probable that in such cases the digestive liquids exercise a less solvent effect upon the toxic mixture. Ordinarily, digestion in insects is exceedingly rapid. Among caterpillars, for instance, feeding is often almost continuous, and twenty-four hours are sufficient to pass through the entire diges- tive system food two or three times the weight of the larvae themselves. Fig. i6. Heart of a stag-beetle, showing the wings and chambers : at the side, the interior ot a chamber, to show the valves. Insects have no system of arteries and veins, and only one real blood-vessel, which serves also as the heart. This, as has been
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