tHE DEVELOPMENT OF ADMETUS PUMILIO. 617 



appearance of these embryos. They appear in almost every 

 respect similar to the embryos o£ the fourth stage^ and the 

 description of those embryos only requires a few additions 

 to be perfect for the embryo of the fifth stage. 



In the first place we must remark the median eyes. They 

 are now very deeply pigmented, except in a narrow line 

 which separated the two eyes. 



The lateral eyes are now also visible ; they resemble Y- 

 shaped marks on both sides of the median eyes. This is 

 caused by the pigment being deposited between the single 

 ocelli, which are three in number. The margin of the fold 

 carrying the median eyes is also more distinctly visible than 

 in the fourth stage. 



1. The Skins. — No important change can be observed 

 in the skins since Stage IV. 



2. The Coelom. — The coelom has undergone many changes 

 since Stage IV. It lias, for instance, given rise to the 

 muscles, of which at least two sets are to be distinguished. 

 A dorso-ventral muscular system has followed the foldings of 

 the coelom, and now consists of a paired muscle in each 

 segment, running from the carapace to the ventral side, 

 except perhaps in the first two segments of the cephalo- 

 thorax. The other set consists of the intersegmental muscles. 

 These run parallel to the surface, from segment to segment. 

 The walls of the coelom also take part in building up the 

 mid-gut. On the ventral side of the abdomen we also find 

 the genital cells lying inside the coelom, as will be described 

 further on. 



3. The Lateral Organ. — The lateral organ is still to be 

 found, but it seems to me to have ceased to have any fuuction. 

 Superficially it seems to be in the same state as it was in the 

 fourth stage ; it is only on cuts that the difference is remarked. 



Sections show that the lumen of the lateral organ is no 

 longer directly connected with that of the rest of the body, 

 and with the base of the fourth extremity in particular. 



The cells which at a less mature stage formed the walls of 

 the lateral organ have died ott', and it is only here and 



