156 



THE BIOLOGY OF INSECTS 



Fig. 41.— Formation of the Mid-gut (mesenteron) in various Insects. 

 A, Longitudinal section through front region of Embryo of Mason Bee 

 (Chalicodoma). B, Similar section through same region of Embryo of 

 Leaf-beetle (Donacia). C. Longitudinal section through central part of 

 digestive tract of Larval Dragon-fly (Epitheca). ec, ectoderm ; m, 

 mesoderm ; en, endoderm ; er (in B), rudiment of mid-gut (regarded as 

 ectodermal) ; b (in A), boundary of endoderm and mesoderm ; v (in 

 C), vitellophags (yolk-devouring cells) : s, stomodaeum (forming mouth 

 and fore-gut ; me, mJd-gut ; p, proctodaeum (forming hind-gut). X about 

 500. A, after J. Carri^re and O. Biirger (Nova Acta Leopold-Carol. 

 Akad. Ixix, 1897). B, after K. Friederichs {lb. Ixxxv, 1906). C, after 

 H. yon Tschuproff {Zool. Ans. xxvii, 1903). 



