GENERATION OF INSECTS. 419 



which forms the sting, and this, as the defensive instrument of the 

 nursing female, has a certain relation to the well-being of the young. 

 Many insects not only provide the germ with the nutritive vitelline 

 mass, or the material for the first development of the embryo, (if, 

 indeed, the parent can be said to be concerned in that supply which 

 is the result rather of a series of spontaneous fissions with an inherent 

 power of assimilation of the primitive germ-cell itself,) but, in some 

 cases, the parent having selected a fit place for the deposition of her 

 precious burthen, continues the maternal office by placing near the 

 ovum the kind of food which the larva will necessarily require in 

 order to complete its growth. 



Some insects, as bees and ants, feed the larvae ; supply them with 

 the required food from time to time, as nurses satisfy the cravings of 

 a child ; but these cares seldom devolve upon the mother in the insect 

 class : they are performed by a distinct race of individuals, of the 

 feminine sex, but incapable themselves of exercising the procreative 

 faculty. 



The mother ear-wig, however, attends to and broods over her eggs 

 during the whole period of larval development, turning them and re- 

 moving them from place to place, according as the locality may 

 happen to be of the required warmth or moisture. 



The forms of the eggs of insects are very variable : often beautiful 

 and regular, like the seeds of plants ; sometimes very singular ; 

 always perfectly adapted to the required conditions for the develop- 

 ment of the future insect. The eggs are cylindrical in Bombyx 

 everia ; conical, with tuberculate ribs, in Pontia napi ; hemispherical 

 in Bombyx dumeti ; lenticular in Noctna psi ; cup-shaped in Orgyia 

 antiqua; flask-shaped in Culex pipiens ; petiolate in Hemerobius 

 perla ; provided with diverging processes like ears in Scatophaga 

 putris, to prevent their sinking too deep in the soft dung ; provided 

 with a special adaptation for floating in some aquatic insects ; with 

 numerous other modifications. 



When impregnation has taken place, the germ yolk becomes con- 

 densed, as in the Ascaris, receding a little from the vitelline mem- 

 brane at its poles. The impregnated germ-cell propagates itself at 

 the expense of part of the yolk, forming an oblong germ-mass, of a 

 hyaline character, and corresponding to the ventral side of the future 

 embryo. From the peripheral part of this, the cell-progeny extends 

 until the whole of the vitelline mass becomes invested by a stratum 

 of minute and nucleated cells. The first phases of development have 

 been well observed by Herold* and Kolliker: the latter gives the 

 following account of the process in the Chironomus tricinctus.\ The 

 * CCXLI. t CCLXIV. 



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