Mx 



SchwK 



Twin embryos in the insect Platycnemis. The embryonic rudiment was split 

 into two unequal portions at an early stage ; the larger portion has produced an 

 apparently normal embryo, but within it (stippled) is the dwarf embryo produced 

 from the smaller portion, which is inside-out (see text). It has become enclosed 

 within the larger embryo as a result of the upgrowth of the sides of the latter ; the 

 direction of upgrowth is shown by the dotted line arrows. This process was 

 too strong for the sides of the smaller embryo, which were forced to follow suit 

 and to fuse ventrally instead of dorsally, thus enclosing the limbs within a closed 

 cavity lined by the outer surface of the epi4ermis. The ventral nerve-cord of the 

 second abdominal segment of the larger embryo is in contact with that of the 

 first abdominal segment of the smaller embryo, which thus appears larger. 

 For explanation of lettering, see fig. 60: capital letters refer to the larger 

 embryo, small letters to the smaller embryo. In addition: Abd^, ist abdominal 

 segment; Bm, nerve cord; F, fibre-tracts; R, dorsal wall. (From Seidel, Biol. 

 Zentralbl. xlix, 1929.) 



