. Text-book of embryology. Embryology. VIII AETHEOPODA 269 and intestine. The calk on the stomodaeal side elongate so as to block the cavity of the oesophagus: they cast out refractive granules, and then, at the final moult, flatten out and form the lining of the adult oesophagus. The cells on the mid-gut side of the valve multiply very rapidly and form a plug completely obliterating the lumen of the mid-gut. The old mid-gut, epithelium is stripped off from its base- ment membrane and is devoured by amoebocytes penetrating from the body-cavity. The whole mid-gut is shortened till it is about o
. Text-book of embryology. Embryology. VIII AETHEOPODA 269 and intestine. The calk on the stomodaeal side elongate so as to block the cavity of the oesophagus: they cast out refractive granules, and then, at the final moult, flatten out and form the lining of the adult oesophagus. The cells on the mid-gut side of the valve multiply very rapidly and form a plug completely obliterating the lumen of the mid-gut. The old mid-gut, epithelium is stripped off from its base- ment membrane and is devoured by amoebocytes penetrating from the body-cavity. The whole mid-gut is shortened till it is about one foui-th of its former length, but Poyarkoff could not determine how this comes about. Then a new provisional epithelium is reconstituted. Fig. 213.—Portions of sections through the valve separating stomodaemn from mid-gut in the larva of Galerucdla iilmi. (After Poyarkoff.) A, in the well-developed larva. B, in the larva on the point of metamorphosis, cut, cuticle lining the stomodaeum ; Lend, larval endoderm ; , pupal endoderm ; stom, atomodaeum ; v, valve. from some of the cells forming the plug. This epithelium lasts during the pupal stage, at the close of which it is thrown off and the definitive epithelium of the mid-gut is formed from other cells of the plug which have hitherto remained undifferentiated. The epithelium lining the hind-gut or proctodaeum behaves very much like that lining the stomodaeum; the cells cast out granules and then flatten, in other words the basal part of each cell rejuvenates itself. Then the folds in the proctodaeum flatten out and the cells become cylindrical; this shape they retain in the pupal stage, but when the adult stage is reached these cells flatten out again. The salivary glands of the larva are entirely destroyed by amoebocytes, but new salivary glands are formed in the pupa when it is three days. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - co
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