DEVELOPMENT 



345 



or aperture of the stomodaeal depression (Fig. 90) three eleva- 

 tions appear, the rudiments of the antennules (a^), antennae 

 (a^), and mandibles (m) : in front of them is another pair 

 of elevations on which the eyes (A) subsequently appear. 



Fig. 90. — Early embryo of Fresh-water Grayfish in the nauplius 

 stage. 



A in the upper part of the figure is the eye : /, the labrum overhanging 

 the mouth, on each side of which are the rudiments of the antennules 

 {a^), antennae (a^), and mandibles (w) : behind them is the rudiment of 

 the thorax and abdomen (7!<4)with the anus{j4). The rudiments of 

 the first three pairs of ganglia {G, gc?, gm) are seen through the trans- 

 parent ectoderm. 



(From Lang, after Reichenbach. ) 



An unpaired elevation {TA) behind the mouth, and having 

 the anus {A) or aperture of the proctodseal depression at its 

 summit, is the rudiment of the thorax and abdomen. The 

 embryo is now called a nauplius. Many Crustacea are 



