The eggs of some insects are fairly transparent, and the process of development in them can, to a certain extent, be observed by simple inspection with the microscope; a method that was used by Weismann in his observations on the embryology of _Chironomus_. There is a moth (_Limacodes testudo_), that has no objection to depositing its eggs on glass microscope-slides. These eggs are about a millimetre long, somewhat more than half that width, are very flat, and the egg-shell or chorion is very thin and perfectly transparent. When first laid the contents of this egg appear nearly homogeneous and evenly distributed, a finely granular appearance being presented throughout; but in {153}twenty-four hours a great change is found to have taken place. The whole superficial contents of the egg are at that time arranged in groups, having the appearance of separate rounded or oval masses, pressed together so as to destroy much of their globular symmetry. The egg contents are also divided into very distinct forms, a granular matter, and a large number of transparent globules, these latter being the fatty portion of the yolk; these are present everywhere, though in the centre there is a space where they are very scanty, and they also do not extend quite to the circumference. But the most remarkable change that has taken place is the appearance in the middle of the field of an area different from the rest in several particulars; it occupies about one-third of the width and one-third of the length; it has a whiter and more opaque appearance, and the fat globules in it are fewer in number and more indistinct. This area is afterwards seen to be occupied by the developing embryo, the outlines of which become gradually more distinct. Fig. 83 gives an idea of the appearance of the egg about the middle period of the development. In warm weather the larva emerges from this egg ten or eleven days after it has been deposited. [Illustration: FIG. 83.—A, Egg of _Limacodes testudo_ about the middle of the development of the embryo; B, micropyles and surrounding sculpture of chorion.] The period occupied by the development of the embryo is very different in the various kinds of Insects; the blowfly embryo is fully developed in less than twenty-four hours, while in some of the Orthoptera the embryonic stage may be prolonged through several months. According to Woodworth the blastoderm in _Vanessa antiopa_ is complete in twenty-four hours after the deposition of the egg, and the involution of the ventral plate is accomplished within three days of deposition. METAMORPHOSIS.