5-46 



INSECTA. 



folds are then forined ; these lead to the formation of the embryonic 

 membranes, whidh are so characteristic of insect development. In 







F:o. 455. Development of the embryo of HytJrojiJiilui piceus (after Kowalovski). a, Shield- 

 like ventral plate With raised edges. It, The edges are already growing together in the 

 middle, c, The groove is almost entirely closed. <f, The tail fold of the embryonic 

 membranes has grown over the posterior end of the closed groove and is gradually 

 extending forward ; Am, Amnion. e, The embryonic membranes have almost entirely 

 grown over the embryo. /, The embryonic rudiment beneath the completely closed mem- 

 branes ; with seventeen primitive segments : El, Procephalic lobes ; A, antenna?, g. The 

 ventral plate extends along the whole length of the ventral surf nee. The bi-lobed upper lip 

 is present, also the antenna 1 , (.-I) the jaws, and the first rudiments of the legs; rudimentary 

 appendages are present on the seventh segment ;is prominences. On the abdominal 

 segments there are round invaginations, the first rudiments of trachea 1 ; there is a 

 longitudinal groove from month to anus, li, The ventral plate covers the whole ventral 

 surface of the ovum ; the openings of the invaginations (stigmata) have become small ; 

 rudimentary extremities are still present on the first abdominal segment. The ganglia 

 of the ventral chain have appeared. /.Viewed from the dorsal surface the so-called 

 dorsal plate has closed up to a tube; Oe is its opening. A-, The embryo just before- 

 hatching seen from the ventral side. 



Ifi/'lropli'dns these folds grow together over the ventral plate from 

 behind forwards, and fuse with one another, so as to give rise to an 



