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ANNUAL, REPORT SMITHSONIAN INSTITUTION, 1925 



the tenth) become the cerci {Cer), when these organs are present. 

 In some of the lower forms of insects there are rudimentary ap- 

 pendages in the adult stage on some of the first seven segments of 



Fi«. 10. — Three methods by which the insect embryo becomes 

 protected within the egg 



A, embryo (Emh) of a springtail (Isotoma cincrea) curved 

 into the yolk on under side of egg. (Figure from Phillp- 

 tschenko.) 



B, C, embryo of Leplsraa (a flsh moth) : first (D), at early 

 stage when deeply sunken into yolk near posterior end of egg, 

 the opening of the cavity closed to a small pore (a) ; and 

 second (C), in later stage when partially revolved to out- 

 side of egg, In which position it completes its development. 

 (Figures from Heymons.) 



D-F, diagrammatic lengthwise sections of an egg in which 

 the embryo revolves roar end first into the yolk (D), becom- 

 ing entirely shut in the latter (E) in reversed and inverted 

 position, and then again revolves to surface (F) in original 

 position before hatching. 



G-I, diagrammatic cross-sections of an egg In which embryo 

 becomes covered by meml)ranes originating In folds of the 

 blastoderm around its edges (G, b), the folds extending beneath 

 the embryo (IT), and finally uniting to form two membranes 

 (I), the outer the serosa (Ser), the inner the amnion (Am). 



the abdomen, and the caterpillars have tubular legs on this part of 

 the body (fig. 28), which are perhaps true abdominal appendages 

 of a primitive structure. 



