THE SCULPTURING OF THE EGG-SHELL 



521 



FIG. 494. Eggs of Phasmidae : A, Lonchodes 

 bodi. B, Plaiy crania edulix. C, Ilaplvpus grayi. 

 Phylliwn siccij/'olium. After Kaup, from Sharp. 



D, 



While the yolk-membrane is usually a completely homogeneous, 

 thin, structureless membrane, the chorion or shell of the egg is 

 usually covered with a network of ridges enclosing polygonal areas, 

 varying in shape accord- 

 ing to the species or 

 genus. These external 

 markings are due to the 

 impress of the cellular 

 structure of the epithe- 

 lium of the ovarian 

 follicle. 



In the chorion of the 

 cockroach the surface 

 appears to be finely 



granular, the finest granules being arranged in large, more or less 

 regularly hexagonal areas, which are bounded by narrow, dark 

 spaces, containing somewhat larger though less dense granules. The 

 surface of the eggs of certain Phasmids are variously sculptured 

 (Fig. 494). 



The true structure of the chorion can only be, as Wheeler observes, seen in 

 cross-sections, as shown by Blochmann, and also by Wheeler. The chorion 

 consists of two chitinous laminae kept in close apposition by means of numerous 

 minute trabeculse or pillars. It is the ends of these pillars that look like gran- 

 ules. In the spaces between the hexagonal areas, the trabeculse are more 

 scattered and individually thicker than those of the hexagons. 



These markings are of singular beauty and complexity in the eggs 

 of many Lepidoptera, whose ova are variously ribbed, forming a 

 beautiful fretwork of raised lines (Figs. 495 

 and 496), while in the Diptera and Hymenoptera 

 the chorion is less solid, and 

 usually smooth under low 



FIG. 495. Egg of cotton-worm moth, Aletia : a, top view, showing FIG. 496. Egg of D<t- 

 the micropyle. After Comstock. nais rchippUH. After 



Kiley. 



powers. The exochorion of the egg of the house and meat fly (C. 

 vomitoria) is pitted with elongated hexagonal depressions, which cross 

 the egg transversely. That of the honey-bee is also divided into 

 long hexagonal areas (Fig. 497). 



