168 



EMBRYOLOGY OF INSECTS AND MYRIAPODS 



the cuticula has formed, a deep meridian furrow (/r) develops around the 

 embryo, passing behind the dorsal organ (Fig. 70). In addition to the 

 meridian furrow, shallow wrinkles appear on the surface of the embryo. 



Fig. 70. — Isotoma. Longitudinal section. Development of meridial furrow (Jr). {do) 

 Dorsal organ, {ect) Ectoderm, {gc) Germ cells, (i/) Inner layer, (j/c) Yolk cell. 



As the meridian furrow deepens, the dorsal organ is swung out of position 

 (Fig. 71, do). The cuticula {cut), designated by Claypole (1898) as the 

 first crenated membrane, now loosens and lies free between embrvo and 



Fig. 7\. — Isotoma. Longitudinal section. Formation of first crenated membrane {cut), 

 {do) Dorsal organ, {fr) Furrow, {yc) Yolk cell. 



chorion, and a new cuticula is formed. The chorion then ruptures, and 

 the embryo expands, causing the meridian furrow and all wrinkles to 

 smooth out, the chorion {ch) adhering cap-like in two sections to the 



