We give some figures, taken from Weismann and Graber, of the imaginal rudiments existing in the larvae of _Muscidae_. Although by no means good, they are the best for our purpose we can offer to the reader. Other figures will be found in Lowne's work on the blowfly now in course of publication. Weismann's paper[104] is now thirty years old, and, when it was written, he was not aware of the intimate connexion the rudiments have with the integument; this has, however, now been demonstrated by several observers. Pratt states[105] that the formation of the imaginal discs in _Melophagus ovinus_ takes place in the later stages of the embryonic development, and after the manner formerly suggested by Balfour, viz. invagination of the ectoderm. [Illustration: FIG. 88.—Median longitudinal section through larva of blowfly during the process of histolysis. (After Graber.) Explanation in text.] Both the regenerative buds and the rudimentary sexual glands are known to be derived directly from the embryo; neither of them undergoes any histolysis, so that we have in them embryonic structures which exist in a quiescent condition during the period in which the larva is growing with great rapidity, and which when the larva has attained its full growth and is disintegrating, then {168}appropriate the products of the disintegration so as to produce the perfect fly. Our Fig. 88, taken from Graber, represents a longitudinal median section of a full-grown larva of _Musca_, in which the processes of metamorphosis are taking place. The position of some of the more important imaginal rudiments is shown by it: _b^1_, _b^2_, _b^3_, rudiments of the three pairs of legs of the imago; _an_, of antennae; between _an_ and _w_, rudiment of eye; _w_, of wings; _h_, of halteres; _f_, fat-body; _d_, middle of alimentary canal; _n_, ventral chain; _st_, stigma; 6, 7, sixth and seventh body segments. PHYSIOLOGY OF METAMORPHOSIS. Many years ago, Harvey perceived the probable existence of a physiological continuity between the earlier and later stages of the Insect's life. Modern investigation has shown that in the blowfly a remarkable analogy exists between the conditions of the pupa and the egg. The outer shell of the pupa corresponds to the chorion or egg-shell, and the delicate outer membrane of the pronymph to the oolemn or lining membrane of the egg; the creamy matter corresponds with the yolk, and the regenerative buds are analogous to the formative portions of the developing egg. The process of histolysis as carried out by the phagocytes of the later life appears also to find a parallel in the vitellophags of the embryonic life.[106] It appears probable that the physiological processes of the post-embryonic metamorphosis may be essentially a repetition—or an interrupted continuation—of those of the embryonic period.