192 



PHILIP P. CALVERT. 



(fig. 33B). The cavity of this tube is the amnion cavity ; its inner 

 blind end is directed towards the anterior pole of the egg, which it 

 approaches more and more as the tube increases in length. The 

 blind end is what will hereafter be the tail end of the embryo, and 

 at this stage of development, is much nearer the anterior than the 

 posterior pole. The walls of this tube are, from their mode of origin, 

 continuous with the uninvaginated parts of the ventral plate ; as the 

 tube increases in length, that part of its walls nearest the dorsal sur- 

 face of the eirg steadilv diminishes in thickness until it forms a mere 



Fig. 34. 



Three later stages of the embryonic development of Calopteryx, showing the turning 

 of the embryo within the shell (after Korschelt and Heider, based on Brandt). 

 The egg-membranes are shown here. 



u, opening of the amnion cavity through 



which the embryo passes. 

 ab^ hind part of the abdomen. 

 am, amnion. 

 at, antenna. 

 md, mandible. 



mx^, first maxilla. 



;«j,-2 second ma.xilla (half of labium). 



oe, beginning of oesophagus. 



/'i P-^P'i> first, second and third leg. 



se, serosa. 



V, front head. 



membrane — \\\q amnion ; that part of the wall nearest the ventral 

 surface of the egg is not thinned, and gives rise eventually to the 

 entire ventral surface of the embryo and the paired appendages, 

 including those of the head (fig. 33C). 



Meanwhile, the uninvaginated portions of the ventral plate are 

 gradually reduced to a sharjfly circumscribed area in front of the 

 mouth of the amnion cavity, and become divided into two bilaterally 



