402 



CUMPARATIVE ANATOMY 



CHAP. 



segments with the rudiments of their extremities are continually differentiated 

 anteriorly (but apparently posteriorly, since the rudiments of the thoraco-abdomen 

 are bent forward). At this [F) stage the rudiments of the ma.xillar segments and 

 of the first maxillipedal segment are already present. The hind-gut has become 

 longer, and with its blind end touches the primitive enteric sac (mid-gut). On each 



Fig. 274.— Astacus fluviatilis, embryo wltli tlie rudiments of all tlie limbs.— The thoraco- 

 abdomen, with the last 4 pairs of thoracic feet out off and laid back, ad, Antennal glands ; t^■tg, 

 4th.8th pair of thoracic feet (ambulatory feet) ; (j, chelate feet ; oft, abdomen ; T, telson (after 

 Beiohenbaoli). 



side the thoraco-abdomen is bordered by a curved integumental wall, the rudiment 

 of the cephalo-thoracic shield. 



Stage G. Embryo with rudiments of maxillipedes (Fig. 277).— The thoraco- 

 abdomen elongates in a longitudinal direction and shows at the end which is 



