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TEXT-BOOK OF ENTOMOLOGY 



FIG. 519. Three embryonic stages of Calopteryx : am, 

 ainnion ; g, edge of the ventral plate ; ps, germ of primitive 

 band ; se, serosa. After Brandt, from Balfour. 



at: 



FIG. 520. Three farther stages of growth of Calop- 

 teryx. B and C show the inversion of the embryo: <i. 

 opening of the amniotic-cavity. out <>f which the embryo 

 emerges ; nb, abdomen; am, ainnion : at, antenna: ;//. 

 mandible; in,r l , n/y-, 1st and 'Jd maxilla': '. n->i>ph:igns : 

 P*< P*t P a , l<-'f- r ^ : " ^i-i-usa ; r, anterior cud of the priuii- 

 tive streak. After Brandt, from Balfour. 



life. There is no revolution 

 of the embryo. The embry- 

 onal membranes arise through 

 the formation of folds. 



In insects with an invagi- 

 nated primitive band, of which 

 the Odonata afford examples, 

 the first rudiment of the 

 primitive band is in the form 

 of a ventral plate of slight 

 extent passing ventrally in 

 the hinder half of the egg, in 

 whose posterior section a pro- 

 cess of invagination (Fig. 518, 

 -4, M), soon occurs. The 

 cavity of this invagination is 

 the first indication of the 

 amnion-cavity (Fig. 518, B, 

 a&), while its wall in its 

 thickened ventral part (K') is 

 concerned in the formation of 

 the primitive band, and, in its 

 dorsal thin part, in the forma- 

 tion of the amnion (B, (7, am). 



Revolution of the embryo 

 where the primitive band is 

 invaginated. At first the 

 head-end of the embryo is 

 directed towards the posterior 

 end of the egg, as in dragon- 

 flies (Fig. 518). Also that 

 surface of the primitive band 

 which afterwards faces the 

 ventral, is at first turned 

 towards the dorsal side of the 

 egg. In order to bring the 

 primitive band into the later 

 relations, there must occur 

 the process of revolution, or 

 turning, of the embryo. The 

 somewhat advanced embryo 

 of the Odonata, after the ap- 

 pearance of the head and 

 thoracic appendages, under- 

 goes a rotating motion around 

 its transverse axis, and at the 

 same time turns out of the 

 amniotic cavity (Fig. 520, B). 

 This process is so managed 

 that near the head-region, the 

 ainnion and serosa, there 

 closely situated to each other, 

 are fused together, and at this 



