"It is often necessary to keep pupæ over winter, for a large proportion of insects pass the winter in the pupal state. Hibernating pupæ may be left in the breeding-cages or removed and packed in moss in small boxes. Great care should be taken to keep moist the soil in the breeding-cages, or the moss if that be used. The cages or boxes containing the pupæ should be stored in a cool cellar, or in an unheated room, or in a large box placed out of doors where the sun cannot strike it. Low temperature is not so much to be feared as great and frequent changes of temperature. "Hibernating pupæ can be kept in a warm room if care be taken to keep them moist, but under such treatment the mature insects are apt to emerge in midwinter. [Illustration: FIG. 167.--Lamp-chimney and flower-pot breeding-cage for insects. (From Jenkins and Kellogg.)] "An excellent breeding-cage is represented by fig. 167. It is made by combining a flower-pot and a lantern-globe. When practicable, the food-plant of the insects to be bred is planted in the flower-pot; in other cases a bottle or tin can filled with wet sand is sunk into the soil in the flower-pot, and the stems of the plant are stuck into this wet sand. The top of the lantern-globe is covered with Swiss muslin. These breeding-cages are inexpensive, and especially so when the pots and globes are bought in considerable quantities. A modification of this style of breeding-cage that is used by the writer differs only in that large glass cylinders take the place of the lantern-globes. These cylinders were made especially for us by a manufacturer of glass, and cost from six to eight dollars per dozen, according to size, when made in lots of fifty. "When the transformation of small insects or of a small number of larger ones are to be studied, a convenient cage can be made by combining a large lamp-chimney with a small flower-pot. "_The root-cage._--For the study of insects that infest the roots of plants, the writer has devised a special form of breeding-cage known as the root-cage. In its simplest form this cage consists of a frame holding two plates of glass in a vertical position and only a short distance apart. The space between the plates of glass is filled with soil in which seeds are planted or small plants set. The width of the space between the plates of glass depends on the width of two strips of wood placed between them, one at each end, and should be only wide enough to allow the insects under observation to move freely through the soil. If it is too wide the insects will be able to conceal themselves. Immediately outside of each glass there is a piece of blackened zinc which slips into grooves in the ends of the cage, and which can be easily removed when it is desired to observe the insects in the soil. "_Aquaria._--For the breeding of aquatic insects aquaria are needed. As the ordinary rectangular aquaria are expensive and are liable to leak we use glass vessels instead.