ASELLUS AQUATICUS. 



347 



EMBRYONIC DEVELOPMENT OF ASEI.LCS AQUATICVS. 



In figure 2, the egg is further advancedj showing 

 the molecules of the head, and one of the external 

 lateral appendages. In figure 3, the embryo is seen 

 in front, showing the rudiments of the two pairs of 

 antennte, labrum, five pairs of mouth-organs, and 

 the two lateral external appendages. Figure 4 shows 

 the embryo a little more advanced, and figures 5 and 

 6 the same, with the body stretched out and seen 

 dorsally and laterally, exhibiting the eyes, segments 

 of the body and tail, the latter figure representing the 

 antennae thrown backwards laterally, and the rudiniental 

 legs. At this jieriod tlie enclosed animal does not ex- 

 hibit the slightest voluntarv or involuntary movements, 

 and Rathke consequently regards the Asellus as emerg- 

 ing from the egg in a more imperfect state than any 

 other articulated or vertebrated animal. At fijiures 7 



