The Hog Louse 711 



The follicle epithelium of the egg chamber secretes first the vitelline 

 membrane, which in this case is also the cell membrane of the egg, and 

 then the chorion. According to Gross, of whose work the following is 

 a resum^, the formation of the chorion begins at the posterior end and a 

 thin endochorion and a thicker exochorion are formed. The former 

 appears striated in section and may be porous. The follicle cells are 

 somewhat convex on their inner surface and an imprint of this is left on 

 the exochorion. Up to this time their nuclei have been lying toward their 

 inner surface, and the formation of the epichorion (exochorion of Leuckart) 

 begins as a constriction between the nuclei, and in the indentations so 

 formed appear small, rather regularly rhomboid, chitinous structures. 

 (The egg shell is not formed of true chitin, since it is soluble in potassium 

 hydroxide.) By further constriction of the epithelial cells between the 

 nuclei a system of hollow cavities in communication surrounds the egg, 

 and these become almost filled by a deposition of chitin forming a distinct 

 chitinous lamella (Plate LXVI, 21 and 22). Up to this point a nucleus has 

 rested on each side of the constriction, but now the one between the epi- 

 and exochorions passes through the canal leaving only a tip of protoplasm 

 (Plate LXVI, 23 and 24). The epichorion now moves closer to the eggshell 

 proper, and the pores assume the appearance of rather long canals (Plate 

 LXVI, 25, a); so that looked at from the surface (Plate LXVI, 26), the 

 epichorion appears pierced by numerous canals perpendicular to its surface 

 (Leuckart, 1855:140; stomata of Stevenson, 1905:16). Between these 

 pores is a network of three-sided cavities. During this development the 

 staining properties of the epithelimn have undergone a change; the proto- 

 plasm takes a deep stain, while the nucleoplasm has become transparent 

 and the nucleolus no longer shows .great affinity for stain. 



On the operculum there is no epichorion formed and the exochorion 

 is much thickened (Plate LXVI, 25, b). 'The chitin formation extends down 

 the sides of the epithelial cells, but it is an outgrowth from the exochorion 

 and not a separate formation. There are polygonal areas on the lid 

 surrounded by a network whose ridges are much deeper than those on 

 the egg, but, as there is no epichorion here, the two parts do not differ 

 in level. 



The epithelial cells now rapidly degenerate, and characteristic, very 

 darkly stained structures, like broken circles, are seen in their protoplasm. 

 On the operculum these are attached to the ridges and extend lengthwise 



