234 



AYERS ON THE DEVELOPMENT 



Fig. 



A living egg 

 treated with caustic 

 soda. The three egg 

 membranes are sep- 

 arated from each 

 other by the action 

 of the reagent. 

 1.— Vitelline mem- 

 brane. 2. — Second 

 chorion. 3. — First 

 or outer chorion. 

 X 15. 



tact with it, quickly dissolves, exposing the egg contents. The folds or grooves of the 

 inner chorion are never so numerous nor so large as those of the external layer. The 

 inner membrane is much thinner than the outer one and quite transparent, so that by the 

 use of caustic soda to remove the outer chorion one is able to make the otherwise opaque 

 eo-ff transparent enough for the study of the embryo in the fresh state. On removing the 

 micropylar cap by means of caustic soda, there appear on the inner 

 chorion beneath this cap polygonal areas with raised edges which fit into 

 corresponding grooves in the inner surface of the cap. The inner chorion 

 is more stainable than the outer, and is sometimes indented opposite the 

 nuclei of the serosa. 



The micropylar apparatus 1 belongs chiefly to the outer chorion and some- 

 times comes off [with this layer when it ruptures. In the region of its 

 fusion with the outer chorion it is composed of polygonal scales or areas, 

 which 'gradually become more prominent as they approach the apex of the 

 cone. From the upper angle of each area is given off a thickened protu- 

 berance or papilla into which the intermediate canal between two adjacent 

 areas is continued as a distinct lumen. The papillae vary in shape from 



simple scale-like patches to nipple-shaped 

 protuberances or even funnel-shaped en- 

 largements, pi. 20, fig. 11. They are most 

 perfect about one-third the distance from 

 the apex toward the base of the cap. The apex itself is 

 smooth or is furnished with only a few flat scales. Besides 

 furnishing channels for the ingress of the male element, 

 the micropylar cap serves as a thick, roughened plate, 

 against which the insect may push when ovipositing with- 

 out injury to the egg and without danger that the ovipos- 

 itor slip from its place. 



The vitelline membrane is of nearly the same 

 thickness (4-5 /.i) as the outer chorion and of a 

 pale gray color. On surface view it appears 

 finely punctate, while in oj^tical section it pre- 

 sents a radiate structure entirely similar to the 

 zona radiata of other animals. It is readily 

 stained by any dye that stains cell substance. In 

 the fresh egg it is at all times in close contact 

 with the yolk, but in hardened eggs it does not 

 shrink with the embryonic membranes and yolk, 

 and hence is easily removed with the chorion. 



The yolk of the mature egg is composed of two 

 distinct elements, fat bodies and albuminoid 

 masses. The former are of nearly uniform size 

 and are globular in shape. The surface of each 

 sphere is differentiated into a thin pellicle, insolu- 



1 See Leuckart (27) for structure of mieropyle and chorion among Insecta. 



Fig. 10. 

 Diagrammatic sketch of a micropylar scale e> 

 and its thickened angles a', b'. The double 

 outlines a, b represent the edges of neighboring 

 scales separated by a groove. X 600. 



Fig. 14. 



.<»» 



Fig. 15. 



Fig. 14. a.— Fragment of a micropylar papilla showing its 

 lumen, b. — optical section of another papilla. In this one the 

 lumen extends to the vitelline membrane but does not pass 

 beyond it. c, d, e and/.— papillae of different forms. X600. 



Fig. 15. The anterior end of an ovarian egg showing the 

 manner of growth of the micropylar papillae. a and b. — 

 two successive stages, c. — surface view of modified papillae 

 from the lower edges of the cap. d. — tunica propria of the 

 ovariole. e. — (in the upper portion of figure, erroneously 

 marked c) remnant of the cell mass that secreted (V) the 

 micropylar cap. x 50. 



