ASELLUS AQUATICUS. 347 

EMBRYONIC DEVELOPMENT OF ASELLUS AQUATIOUS. 
In 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 
antenne, 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 
antenne 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 
yy 
other articulated or vertebrated animal. At figures 7 
