Fossorial wasps act differently; they never see their young. They lay their eggs in burrows, sunk in the soil and hermetically sealed. The larvæ are hatched underground and are never seen by the mother. Provision sufficient for their development, however, is made in advance. Before depositing eggs, the females sink the burrows, and fill them with the spoils of the chase, which consist sometimes of spiders and sometimes of crickets or other insects. Each species of fossorial wasps preys on a particular kind of insect or on its allies, for the purpose of provisioning the burrows. These wasps are most fastidious in the choice of their food, and behave like collectors whose interest is only in a single or a few species of small animals. Léon Dufour, the well-known entomologist, was much struck by the ability displayed by certain wasps (_Cerceris_, Fig. 3) in seeking out and capturing the pretty beetles of the genus _Buprestis_, which he had great difficulty in finding himself. In making a study of these beetles he collected the material from the burrows of _Cerceris_, and so avoided the laborious task of obtaining them in the natural state of freedom. The burrows were filled with motionless, but perfectly well preserved, _Buprestes_. Although dead Coleoptera dried up in a short time, those recovered from the burrows remained in a good state of preservation for weeks. Léon Dufour came to the conclusion that the _Cerceris_ kill their prey, but inject into them some antiseptic liquid which perfectly preserves their flesh and intestines. [Illustration: FIG. 3.—_Cerceris_ (after Buffon). ]