158 



CRUSTACEA. 



originally formed on that surface of the terminal segment which 

 afterwards becomes the dorsal surface, later it shifts into the space 

 between the two lobes into which the terminal segment soon divides, 



FIG. 81. Embryo of Astacus fluviatilis with the rudiments of all the limbs (Fig. 83, p. 1(53) 

 (after REICHENBACH, from LANG'S Text-book). The thoraco-abdomen, which in reality curves 

 forward ventrally, is cut off and laid back, ad, antemial gland ; a+>, abdomen ; < 4 , first pair 

 of ambulatory limbs (chelate feet); 3 -< 8 , second to fifth pair of ambulatory limbs; T, telson. 



and through this space gradually reaches the later ventral side, and, 

 in this way, its final position. 



Immediately behind the thoraco-abdominal rudiment, at the point 

 where this is connected with the rest of the body, in later stages, an 



