THE AMERICAN ENTOMOLOGIST. 



restless and wander aimlessly about over leaf 

 and limb, and are met by the young 

 females, who partake also of their rest- 

 lessness, and together tliey wander about over the 

 trunk and the limbs of the tree for from 

 seven to ten days, when the females return to 

 the leaves, and the males secrete themselves 

 underneath the rougliened outside bark of the 

 tree and undergo their transformation into the 

 imago. A limited number of thcni return to the 

 leaves and change thereon. From the spines 

 and pores of tlie integument of the body issues a 

 white substance in which the larva is enveloped. 

 This covering soon assumes an oval form, and is 

 composed of threads, the inner coat cemented 

 closely together, while the outer threads are 

 irregularly arranged, althougli the form is re- 

 tained perfectly. The entire cocoon is held in 

 place by attached threads to the bark or leaf. 

 Inside of the cocoon the larva gradually changes 

 from the wingless insect to the mature or winged 

 state, the rostrum disappears and two wings form. 

 The transformation is gradual, the pupa is of a 

 solid red color and measures from g to lo milli- 

 meters long and S to 4 wide. The antennx, 

 eyes, and legs change their form, and, after about 

 fifteen days one end of the cocoon opens and the 

 perfect male comes out ; the opening through 

 which it emerges is circular and covers the entire 

 end of the cocoon. 



Mistakes made by Instinct. — Errors 

 in instinct through the laying, or mis-lay- 

 ing, of their eggs by insects at wrong times 

 or in wrong places were well known to the 

 older entomologists, as the following in- 

 teresting passage from Degeer abundantly 

 proves. I quote from the German trans- 

 lation of Gotze (Abhandlungen zur Ge- 

 schichte, etc., vol. ii, part 2, p. 241, pi. 35, 

 figs. 12 and 13). He has been describing 

 a Saw-fly which spins a double cocoon. 

 Inside one of these double cocoons, with 

 its head sticking out of its own coarctate 

 pupa-case, he found a dead, dipterous par- 

 asite of the Saw-fly ; and he ascribes its 

 death to a mistake of the parent fly in lay- 

 ing her egg on the false caterpillar of the 

 Saw-fly when the latter was too far ad- 

 vanced in its growth. " Its fate," he says, 

 " was a consequence of the mother's over- 

 sight, which seems to have laid her egg too 

 late on the false caterpillar, so that the 

 larva proceeding from it could not attain 

 to its i- ull size before the Saw-fly caterpil- 

 lar must prepare for its transformation, 

 and consequently, unwittingly let itself be 

 shut up in an everlasting prison. It had 

 indeed, gone on to devour the caterpillar. 

 It had changed to a nymph within the red 

 cocoon ; but when it became a fly it could 



not make its way through the double co- 

 coon of the Saw-fly, and must consequently 

 perish. Thus the mother fly had erred in 

 laying her egg, a thing that is not usual 

 among insects, which on every occasion, 

 and especially in the propagation of their 

 species, display always so much diligence 

 and foresight." To this, however, the 

 translator adds in a note : " Nevertheless, 

 examples and instances occur in more than 

 one species, that insects, whether in re- 

 spect of time or place, are frequently wont 

 to err in oviposition. I could wish that 

 people would collect and compare more 

 examples of the like kind. Perhaps we 

 might thereby discover many a secret in 

 the economy of insects that still remains 

 hidden from us." — J. A. Osborne, M. D., 

 Milford, Letterkenny, in Science Gossip. 



How FLIGHT IN INSECTS IS DIRECTED. — 



At a late meeting of the French Academy 

 of Sciences, Mr. Jousset de Bellesme dis- 

 cussed the organs which direct the flight of 

 insects. Insects in general, he contends, 

 cannot change the angle under which they 

 vibrate the wings, because the motory mus- 

 cles of the wings are inserted within that 

 piece of the thorax which supports these 

 organs. Thus the wings of insects are 

 simply motory organs, and the direction of 

 the flight must be due to the function of 

 other organs. Mr. Jousset is led by ex- 

 periment to believe that the direction of 

 the flight is principally determined by the 

 displacement of the centre of gravity. In 

 Coleoptera this displacement results from 

 the position of the elytra, which therefore 

 are the true directive organs ; in Diptcra 

 the halteres supply this function ; in the 

 Grasshoppers the displacement of the cen- 

 tre of gravity depends on the inclination 

 and "redressement" of the greatly developed 

 hind legs ; in Hymenoptera the abdomen 

 modifies the direction of the flight, and in 

 some cases the hind legs assist therein, 

 Only in Lepidoptera and Neuroptera Odo- 

 nata the changing in the direction of the 

 flight depends largely on the wings them- 

 selves, though the abdomen appears, here 

 also, to take part of the function. 



