ASELLUS AQUATICUS. 



347 



EMBRYONIC DEVELOPMENT OF ASBLLUS AQTJATICUS. 



Iii figure 2, the egg is further advanced, 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 

 antennae, 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 rudimental 

 legs. At this period the enclosed animal does not ex- 

 hibit the slightest voluntary 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 figures 7 



