Fig. 165, A-I. — Normal embryonic primordium of the libellulid insect Platycnemis pennipes 

 and results of ligaturing in early stages. A, two lateral areas more densely nucleated than 

 other areas in early stage of normal development; B, later stage with cephalic lobes and region 

 of beginning inversion of posterior end of primordium indicated by denser nucleation; C, re- 

 sult of complete separation of posterior region by ligature in early stages, inhibition of embryo 

 formation; D, E, complete ligature at more anterior levels, embryo formation only posterior 

 to ligature; F, incomplete ligature, head formation anterior, and embryo posterior to ligature; 

 G, incomplete ligature in blastoderm stage anterior to differentiation center, embryo only 

 posterior to ligature; H, incomplete ligature at blastoderm stage in differentiation center, 

 embryos both anterior and posterior to ligature; /, ligature posterior to differentiation center, 

 embryo only anterior to ligature (after Seidel, 19296, 1934). 



