232 AYERS OX THE DEVELOPMENT 



are given surface views of the follicular epithelium in several successive stages of degenera- 

 tion. PI. 20, fig. 14 is from a follicle in which the yolk is being deposited ; pi. 20, fig. 15, 

 from a follicle in which this process is nearly completed ; pi. 20, fig. 16, from a follicle 

 where the chorion is being formed; pi. 20, fig. 17, from the corpus luteum. Fecundation 

 probably takes place while the egg is passing into the vagina, since it is hardly possible 

 that the male element could gain access to the follicles before the chorion is secreted. 



The egg has acquired more than half its normal size before any membrane is to be 

 distinguished surrounding it, consequently it is only in the lower follicles that the process 

 of the formation of the membranes is to be observed. Before the pocket in which the egg 

 lies becomes terminal, the vitelline membrane may be detected as a very delicate, colorless 

 sheet surrounding the yolk. The most of the yolk material is already within this mem- 

 brane, but from its subsequent increase in size it must be inferred that there are further 

 additions to its mass by a process of endosmosis. Later there are deposited about this 

 membrane two others, true chorion laj^ers ; both are derived from the same source as the yolk 

 and by a process almost continuous with that which forms the latter. Both the vitelline 

 membrane and the first layer of the chorion form continuous envelopes, but the second 

 layer of chorion is interrupted at the upper end of the egg and in its place is deposited a 

 micropylar apparatus. Although it is only a modified portion of the chorion 

 and is at its outer and thinner edge in direct continuity with the outer chorion, 

 this apparatus is easily separable as a distinct cap of thickened chitinous 

 processes. The inner layer of chorion, which is deposited by the same cell 

 mass as the outer layer, exhibits but faint indications of the subsequently 

 deposited cap. During the deposition of the layers of the chorion the previ- m 1 r S *iar en 

 ously straight egg becomes curved, with its concave surface facing ventrad. soX ted Tiie' Tmie 

 This curvature fits the egg for the pit made by the ovipositor for its recep- f tbe te<Pan<f"the 

 tion. By examining an infested stem these pits will be seen to be curved. J ™ e ^'action of ale 

 The egg having received its protective membranes is ready for deposition, r ^" e \apMa\°rar- 

 and the epithelium of the terminal follicle, having now become much 1^;, S'fEJftfde'tf 

 reduced in thickness by the production of these layers, forms but a loose the fisure " 

 sac around the egg. The latter on this account passes into the oviduct. On its passage,, 

 through the vagina, the egg is coated by a mucous substance which hardens on exposure 

 to the atmosphere or on contact with the pith of the stem in which it is laid. In the 

 latter case it serves to retain the egg in position. The egg coatings, now five in number 

 may be arranged for convenience of reference as follows : 



1. Mucous coating — structureless — secreted by vaginal mucous glands. 



2. Outer chorion — produced by the follicular epithelium — presents a series of surface 



markings or cracks. 



3. Inner chorion — produced by the follicular epithelium — presents a series of surface 



markings or cracks less numerous and fainter than those of the outer chorion. 



'In the allied Acheta abbreviate, the egg is not curved vided with a micropylar end (?). The eggs are laid in 



and is destitute of a micropylar cap.' The eggs are laid in ground which is rendered hard by sun-bake, so that the 



1 oose earth among the roots of grass. In Caloptenus insect is compelled to drill special cavities for their reception, 

 spretus, according to Packard, the err? is curved and is pro- 



