EPHEMERIDA, ODONATA, PLECOPTERA, ET AL. 



199 



As the yolk diminishes, the walls of the spherules are more clearlj- seen, 

 and soon it is evident that these walls are arranged in such a manner that 

 a provisional mid-gut is formed (Fig. 122), the outer walls (wo) constitut- 

 ing a continuous covering enclosing the yolk mass, the side and inner 

 walls of the spherules (ws) further enclosing the yolk into compartments. 

 While the provisional mid-gut is forming, the end of the stomodaeum is 

 expanding until it finally forms a bulbous sac (stom) extending into 

 the mid-intestine. In a living egg the compartments appear clearly 





stom 



VSP 



Fig. 123. — Libellula. 



prod- 



Dorsal aspect of nine-day living embryo, {prod) Proctodaeum. 

 (stom) Stomodaeum. (ysp) Yolk spherule. 



defined, and the bulbous end of the stomodaeum is apparent as well as 

 the smaller expanded end of the proctodaeum extending into the yolk 

 (Fig. 123). Movement of the mid-gut is evident in a live egg at this 

 stage in development. 



Further reduction of the yolk in the compartments causes their walls 

 to shrink away from the center of the mid-intestine, leaving an irregular 

 lumen extending from the stomodaeum to the proctodaeum (Fig. 124, lu). 

 This lumen is not evident throughout its entire length in Plathemis lydia 

 until shortly before hatching on the fourteenth day. 



The nymph of Plathemis emerges from the egg during the fourteenth 

 day. The newly emerged nymph has a round bulbous head and a long 

 slender abdomen ; its legs remain in the same position under the abdomen 



