. The American entomologist and botanist. , where only a singlelarva can develop, is a striking instance of mis-directed instinct; but we tind a similar i)rodi-gality throughout Nature, for every individualis 80 subject to disasters of one kind or anotherin its struggle for existence, that a provision ofseveral ova is often necessary to insure thefuture development of a single one, just as weoften sow several seeds of some particular order to insure the growth of a single one. After the Cecropia worm has formed its co-coon, the parasitic larva, which had hithertofed on the fatty porti
. The American entomologist and botanist. , where only a singlelarva can develop, is a striking instance of mis-directed instinct; but we tind a similar i)rodi-gality throughout Nature, for every individualis 80 subject to disasters of one kind or anotherin its struggle for existence, that a provision ofseveral ova is often necessary to insure thefuture development of a single one, just as weoften sow several seeds of some particular order to insure the growth of a single one. After the Cecropia worm has formed its co-coon, the parasitic larva, which had hithertofed on the fatty portions of its victim, nowattacks the vital parts, and when nothing butthe empty skin of the worm is left, spins itsowu cocoon, which is oblong-oval, dark browninclining to bronze, and spun so closely andcompactly, that the inner layers when separatedhave the appearance of gold-beaters skin. Ifwe cut open one of these cocoons soon after itis completed, we shall find inside a larfee fatlegless grub (Fig. 64), which sometimes under- [Pig. 64.]. Color—Yellow goes its transformations and issues as a fly inthe fall, but more generally wails till the fol-lowing spring. TuE Cecuoiia Tachina Fly.—The Ichneu-mon fly last mentioned usually causes a dwarfedappearance of the worm which it infests, andparasitized cocoons can generally be distin-guished from healthy ones by their smallersize. The larvie of the Tachina fly, which wenow introduce to our readers, as parasitic onthe (ecropia worm, seem to produce an exactlyopposite eflecl—namely, an undue and unna-tural growth of their victim. In the beginningof September, 186G, we received from llocktord,Ills., an enormous Cecropia worm. It measuredover four inches, was a full inch in diameter,and weighed nearly two ounces; but like manyother large specimens which we have siuce seen, it was covered with small oval opaque whiteegg-shells, clnsters of four or five occurring onthe back of each segment, invariably depositedin a transverse d
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