OLIGOENTOMATA AND APT I LOT A 



169 



surface of the embryo (Fig. 72). At the time the chorion ruptures, the 

 second cuticle {cut 2) of the embryo also loosens to form the second 

 crenated membrane of Claypole (1898). 



After the chorion has ruptured, it is apparent that the embryonic 

 rudiment (germ band) forms a belt around the yolk, the head and tail 

 ends nearly meeting at the dorsal organ (Fig. 72). The cells of the germ 

 band are columnar and two-layered, the outer forming the ectoderm; 

 the inner, the inner layer. The cells of the original blastula which lie 

 on the sides of the egg have become flattened and thinner and have lost 



Fig. 72. — Isotoma. Rupture of chorion {ch). {cut 1, cut 2) First and second crenated 

 membranes, (gc) Germ cells. (M) Head lobes. 



the inner-layer cells which have migrated into the inner layer of the germ 

 band (Figs. 73, 74). According to Uzel, the germ band of Campodea is 

 formed in a similar manner. Since the flattened cells on the sides 

 together with the germ band form an envelope covering the yolk, and 

 since they are a part of the original blastula, these flattened cells may be 

 called the "amnioserosa." The germ band now shows distinct head 

 lobes (Fig. 76, hi), a broad tail lobe, and four body segments. After the 

 rupture of the chorion, which takes place about five days after egg deposi- 

 tion, the dorsal organ takes on another character. The cells themselves 

 retain their previous appearance, with vacuolate inner and a fibrillar 

 outer part, but are more expanded with the outer fibrillar part projecting 



