. The Cambridge natural history. Zoology. METAMORPHOSIS 167 Imaginal Discs.—TKe 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 Klinckel d'Herculais,^ are distinguished by any important character from other buds or portions of regenerative tissue that, according to Kowalevsky,^ Korschelt and Heider,^ and others, exist in other parts of the body, does not appear to
. The Cambridge natural history. Zoology. METAMORPHOSIS 167 Imaginal Discs.—TKe 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 Klinckel d'Herculais,^ are distinguished by any important character from other buds or portions of regenerative tissue that, according to Kowalevsky,^ Korschelt and Heider,^ and others, exist in other parts of the body, does not appear to be at present ascertained. "We give some figures, taken from Weismann and Clraber, of the imaginal rudiments existing in the larvae of Musciclae. Although by no means good, they are the best for our pm'pose 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 * 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, how- ever, now been demonstrated by several observers. Pratt states * that the formation of the imaginal discs in Melopliagus ovinus takes place in the later stages of the em- bryonic development, and after the manner formerly suggested by Balfour, viz. invagin- ation of the ectoderm. 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 Pig. 88. — Median longi- we have in them embryonic structures tudinai section through 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. larva of blowfly during the process of histo- lysis. (After Grater.) Explanation in text. ^ Secherches Org. des Volucelles, 1875, p. 143. ^ Zeitschr. wiss. Zool. xlv. 1887, p. 587. ^
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