These buds, of which about sixty or upwards have already been detected, undergo {166}growth as they are liberated, and so the new creature is formed, the process of growth in certain parts going on while destruction is being accomplished in others. Considerable discrepancy prevails as to the extent to which the disintegration of some of the tissues is carried. [Illustration: FIG. 87.—Imaginal discs of _Muscidae_ in process of development: A, Brain and ventral ganglion of a larva 7 mm. long of _M. vomitoria_; _v_, ventral ganglion; _c_, cephalic ganglion; _h_, head rudiment; _vc_, portion of ventral chain; _pd_, prothoracic rudiment; _vc_{3}_, third nerve; _md_, mesothoracic rudiment: B, mesothoracic rudiment, more advanced, in a pupa just formed of _Sarcophaga carnaria_, showing the base of the sternum and folds of the forming leg, the central part (_f_) representing the foot: C, the rudimentary leg of the same more advanced; _f_, femur; _t_, tibia; _f_{1}_, _f_{5}_, tarsal joints: D, two discs from a larva 20 mm. long of _Sarcophaga_, attached to tracheae; _msw_, mesonotal and wing-rudiment; _mt_, metathoracic rudiment: E, _r_, mesothoracic rudiment of a 7 mm. long larva attached to a tracheal twig. (After Weismann and Graber.)] According to Kowalevsky[99] it would appear that after the phagocytes have become loaded with granules they serve as nutriment for the growing tissues, and he thinks they become blood-cells in the imago. The process of histolysis has been chiefly studied in the blowfly, and not much is known of it in other Insects, yet it occurs to a considerable extent, according to Bugnion[100] and others, in the metamorphosis of Lepidoptera. Indeed it would almost seem that the processes of histolysis and histogenesis may be looked on as exaggerated forms of the phenomena of the ordinary life of tissues, due to greater rapidity and discontinuity of tissue nutrition. {167}IMAGINAL DISCS.—The imaginal discs are portions of the larval hypoderm, detached from continuity with the main body of the integument, but connected therewith by strings or pedicels which may be looked on as portions of the basement membrane. Whether these discs, or histoblasts as they are called by Künckel d'Herculais,[101] are distinguished by any important character from other buds or portions of regenerative tissue that, according to Kowalevsky,[102] Korschelt and Heider,[103] and others, exist in other parts of the body, does not appear to be at present ascertained.