. Injurious and useful insects; an introduction to the study of economic entomology. Insects; Beneficial insects; Insect pests. ^ Fig. 78.—Pupa- rium of blow-fly THE STRUCTURE OF THE BLOW-FLY 139 finally almost black. Within this hard and dry skin the larva changes to a pupa, and the pupa to a fly. If the pupating insect is examined when the pupa-case is red-coloured, it will be found to contain a creamy fluid, with little visible structure. By the help of carefully pre- pared microscopic sections, it has been discovered that in this stage the larval organs break up, and new (imaginal) organs
. Injurious and useful insects; an introduction to the study of economic entomology. Insects; Beneficial insects; Insect pests. ^ Fig. 78.—Pupa- rium of blow-fly THE STRUCTURE OF THE BLOW-FLY 139 finally almost black. Within this hard and dry skin the larva changes to a pupa, and the pupa to a fly. If the pupating insect is examined when the pupa-case is red-coloured, it will be found to contain a creamy fluid, with little visible structure. By the help of carefully pre- pared microscopic sections, it has been discovered that in this stage the larval organs break up, and new (imaginal) organs take their place. The destruction of the larval structures is effected by the activity of peculiar blood corpuscles (phagocytes) which eat up the muscles, epi- thelial cells, etc., and ultimately transfer their own substance to the growing tissues. The new organs of the fly are developed from special cellular patches, forming part either of the epi- dermis, or of the epithelium of the internal cavities. These centres of development arise by infolding of the epidermis or epithelium. e"nd'osi'ngt^h^"true Such pouches or infoldings can be seen in a ^"jP^'g ^"^f '=°|,"j simpler form in late larvse of such insects as 'a/vai skin, mag- Chironomus, Lepidoptera, etc., where the larval legs are wanting, or too short to receive the much longer legs of the pupa and imago, the bases of which, as they grow, become telescoped into the body, while the tip may be still en- closed within the larval legs. Should the legs, wings, mouth-parts, and other similar organs be almost or altogether undeveloped in the larva, but large and complex in the fly, the infoldings,'become deeper still, and seem to lose all connection with the epidermis or epithelium to which they belong. This is the case with the blow- fly. The larva has, at most, insignificant rudiments of eyes, feelers, mouth-parts, wings, and legs, while all are of elaborate structure in the fly. Moreover, the alime
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectinsects, bookyear1902
