The time occupied in making this silken dress is, for drone- and worker-larvæ, thirty-six hours. Princesses, who trouble themselves to make only half-cocoons, finish theirs in twenty-four hours. So soon as the grubs are ready for this process, the nurse-bees form over the entrance to each cell a lid made of wax and a sticky substance called propolis; leaving, however, minute perforations for the admission of air. These coverings are darker than the caps of the honey-cells. They are also somewhat convex over worker-larvæ, and over drone-grubs they stand out almost hemispherically. Hence it is easy to distinguish the look of brood cells from that of those containing food-stores. Moreover, the former are situated usually in or near the centre of each comb, while the latter, where the two co-exist, are found near the top. It is very important to learn the difference in appearance between the two, as several points of successful manipulation depend upon the knowledge. [Illustration: Fig. 4.--A. Larva full grown, viewed sideways. B. Larva preparing for pupa state.] _The nymph or pupa._--In this condition the insect is at first semi-transparent, and white, with a yellowish tinge. Hour by hour the various organs of the perfect bee proceed in their development, and become more and more discernible through the thin pellicle enshrouding them. On the head, the eyes and antennæ assume their ultimate size and marvellous structure. The legs and wings are clearly seen folded lengthwise along the thorax and abdomen. The chitinous covering of the body attains increasing firmness, and the colour of the exterior deepens to a greyish brown. At length, in periods varying in the three classes of inmates of the hive, maturity is reached. In the case of queens, sixteen days suffice for complete metamorphosis from the egg to the full-grown insect. Drones require twenty-four days, and workers from nineteen to twenty-two days, according to the warmth of the weather, to go through all their changes. [Illustration: Fig. 5.--Worker Larva and Pupa in Comb.]