OP GENERATION.

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If we take a retrospection of the whole process of the developmentof the germ to the egg we shall find that there are three distinct periodsin its progress. The filiform superior appendage of the egg-tube isthe first, for in it takes place the secretion of the formative matter, andfrom here it descends into the egg-tube as a germen. The remainder,probably albuminous portion, of the secretion, remains, as placentula,between every two egg germs. The second period is the loosening ofthe placentula by copulation. By means of it the internal tunic comesinto close contact with the exterior vascular one, in consequenceof which the ring is formed; and at the same time the impregnation ofthe germ takes place by the male semen imbibed from the placentula.The ring, lastly, is the third period; it promotes, by supplying theplacentula with atmospheric air, its capacity of appearing as a neworganic mass, so that it may be gradually imbibed by the growing egg.The yolk thus becomes perfectly formed, and envelopes itself with itssecond tunic, and then with its shell, which is hardened also by means ofthe air from the ring. The formation of the egg is then completed, andthe period of laying comes, which takes place immediately, to makeroom for a still immature egg. It is from this circumstance that someinsects, namely, those with many egg tubes, for example, the queen bee,require a long time to lay all their eggs, and only in those with bag andbladder-shaped ovaries, which are furnished upon their surface withshort egg-tubes (as, for example, Lytta and Meloe,) can the eggs bealmost all matured at the same time.

§ 211 .

When, after all this procedure, the egg has quitted the maternalsphere, a distinct life, namely, that of the embryo, commences in it.If we first survey the structure of the laid egg we shall observe that itconsists externally of a horny shell, which becomes tolerably hard inthe air, and is in general transparent or colourless, but less frequentlydecorated with particular markings and colours. Beneath this externalcovering lies a second, finer, more delicate membrane, which forms thecase of the fluid contained within the egg. This fluid is the yolk,( vilellas ,) a yellow, whitish, or green, thick, granulated mass, which inPhasma is dotted with purple, and it chemically consists of albumen,some animal glue, a yellow fat oil and sulphate and phosphate of natron*.

* See John’s Chemische Sehrift, vol. ii. p. 112.

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