402 



COMPARATIVE 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 maxillar 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 



Fio. 274. Astacus fluviatilis, embryo with the rudiments of all the limbs. The thoraco- 

 abdomen, with the last 4 pairs of thoracic feet cut off and laid back, ad, Antennal glands ; t 4 -t$, 

 4th-8th pair of thoracic feet (ambulatory feet) ; t, chelate feet ; ab, abdomen ; T, telson (after 

 Reichenbach). 



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 



