"Compartments and polyclones in insect development"

Date:
1973-1975
Reference:
PP/CRI/H/5/11
Catalogue details

Licence: In copyright

Credit: "Compartments and polyclones in insect development". Source: Wellcome Collection.

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    ment or function. There are the histoblasts and the imaginai discs. There are 19 of the latter (9 pairs of discs plus the single ge-fle ¿Wtel disc). -Hiy nf -expe-sitionVie shall concentrate mainly on one pair of these, the so-called wing disc. The left wing disc, within the left side of the larva, produces the left wing of the insect and that part of the left side of the body (the mesonotum and pleurae) next to the wing. The disc is responsible for both epithelium and internal structures but in what follows we shall be concerned in the first instance only with epithelial structures, mainly for technical reasons (they are much easier to score in genetic experiments). The wing disc is first formed before hatching oy the invagination of a small patch of embryonic epidermal cells. These cells remain diploid whgfle the surrounding larval epidermal cells become polyploid. As we shall see there are probably only about 50 cells forming the^isc at this early stage. During the course of larval growth these disc cells divide in all about 10 times to give a total of some 50, 000 cells. T he e s ri - mated growth curve, due to Garcia-Bellido, is shown in Fig. y. At the pupal stage ZV-**- WCU-v— the growth of the disc stops. The disc has now a characteristic size and shape being somewhat like an|invaginatec^ flattened and heavily folded balloonj^the exact struc- ture is difficult to describe clearly and the reader should referto \ diXßXT ' \ W • for what details are known. ^ At metamorphosis a complicated set of cell movements occur which result in the balloon (the disc, that is) being turned inside out so that it can form the adult structure. The wing itself, for example is first formed as a bag from that part of the everted balloon furthest from the neck of the balloon. The bag is then collapsed to form the adult wing which is thus, in broad terms, a single sheet of epithelial cells folded and collapsed to form a double layer of epithelial cells (see Fig. 2). The above description omits much detail which is already known but should enable ,, , in the reader to get a general picture of wing development in Drosophila .