. Zoology : for students and general readers . Zoology. DEVELOPMENT OF INSECTS. 351. Fig. 299.—Embryo of Sphinx much more advanced, h, lieart; g. ganglion ; i, intestine ; m, rudimentary muscular bands mn- ning to tile heart; s, stigma and beginning of a tracliea {i}; rf, a gland. Tlds and Mgs. a95-S96 after Kowalevsky. appendages bud out from the under side of the primitiYe band, and antennae, Jaws, legs, ovipositor (or sting), and the abdominal feet of caterpillars are at first all alike. Soon the appendages begin to assume the form seen in the larva, and just before the insect hatches the l
. Zoology : for students and general readers . Zoology. DEVELOPMENT OF INSECTS. 351. Fig. 299.—Embryo of Sphinx much more advanced, h, lieart; g. ganglion ; i, intestine ; m, rudimentary muscular bands mn- ning to tile heart; s, stigma and beginning of a tracliea {i}; rf, a gland. Tlds and Mgs. a95-S96 after Kowalevsky. appendages bud out from the under side of the primitiYe band, and antennae, Jaws, legs, ovipositor (or sting), and the abdominal feet of caterpillars are at first all alike. Soon the appendages begin to assume the form seen in the larva, and just before the insect hatches the last steps in the tion of the larval form are taken. As to the development of the in- ternal organs, the ner- vous system first origi- nates ; the alimentary canal is next formed ; and at about this time the stigmata and air- tubes arise as invagina- tions of the outer germ- layer. The development of the salivary glands precedes that of the uri- nary tubes, which, with the genital glands, are originally offshoots of the primitive digestive tract. Finally the heart is formed. When the insect hatches, it either cuts its way through the egg-shell by a temporary egg-cut- ter, as in the flea, or the expansion of the head and thorax and the convulsive movements of the body, as in the grasshopper, burst the shell asunder. The serous membrane is left in the shell, but in the case of grasshoppers the larva on hatching is still enveloped in the am- nion. This is soon cast as a thin pellicle. The principal change from the larval to the adult locust or grasshopper is the acquisition of wings. In such insects, then, as the Orthopiera and Hemiptera, in which the adults differ from the newly hatched larva mainly in the posses- sion of wings, metamorphosis is said to be in- complete. In the beetle, butterfly, or bee, the metamorphosis is complete ; the caterpillar, for example, is a biting insect. Fig. 300.— Primitive band or germ of a Sphinx moth, with the segments in- dicated, a
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1879
