124 



PRINCIPLES OF EMBRYOLOGY 



at an early stage of the dispersion of the nuclei, each part forms its own 

 complete embryo. Owing to the extensive movements which take place 

 during development, the relations of these twins to one another may be- 

 come very pecuhar. In one case described by Seidel, a slightly oblique 

 fold had separated the egg into a larger and a smaller portion. Each 





FlGUHE 8.2 



Development of the dragonfly Platyaiemis. Figures a, b, c, and d are sections 

 showing the first three divisions of the nucleus, and the spreading of the 

 daughter nuclei through the egg cytoplasm (the two sister nuclei from a 

 division are joined by a dotted line). In e the nuclei are beginning to reach 

 the surface;/,^ and h are surface-views showing the multiplication of the 

 nuclei to form a blastoderm and their aggregation to produce the germ- 

 band [G.B.). In I the germ-band is being pulled into the interior of the egg; 

 at the stage of Figure ^ nearly the whole embryo (dotted) lies internally. It 

 is then pulled out again, at the same time rotating around its longitudinal 

 axis [k). Note that in its final position (/) its head (H) is again towards the 

 pointed end of the egg. (After Seidel 1929.) 



