The provisions which are made by the different species of insects for protecting their eggs, appear in many cases to be admirably proportioned to the kind of danger and destruction to which they may be exposed. The eggs themselves, indeed, are not so liable to depredation and injury as the young brood hatched from them; for, like the seeds of plants, they are capable of withstanding greater degrees both of heat and cold than the insects which produce them. According to the experiments of Spallanzani, the eggs of frogs that had been exposed to various degrees of artificial heat were scarcely altered in their productive powers by a temperature of 111° of Fahrenheit, but they became corrupted after 133°. He tried the same experiment upon tadpoles and frogs, and found they all died at 111°. Silkworms died at a temperature of 108°, while their eggs did not entirely cease to be fertile till 144°. The larvæ of flesh-flies perished, while the eggs of the same species continued fertile, at about the same comparative degrees of heat as in the preceding instances. Intense cold has a still less effect upon eggs than extreme heat. Spallanzani exposed the eggs of silk-worms to an artificial cold 23° below zero, and yet, in the subsequent spring, they all produced caterpillars. Insects almost invariably die at the temperature of 14°, that is, at 18° below the freezing point.[N] The care of insects for the protection of their eggs is not entirely directed to their preservation in the most favourable temperature for being hatched, but to secure them against the numerous enemies which would attempt their destruction; and, above all, to protect the grubs, when they are first developed, from those injuries to which they are peculiarly exposed. Their prospective contrivances for accomplishing these objects are in the highest degree curious.