ORDER STOMAPODA. 197 



jaw-feet, whether these segments be exterior, or concealed by 

 the testa, and even very small, as is the case with the ante- 

 rior ones. At the level of the first five rings of the abdomen, 

 or of those which carry the natatory appendages, and the 

 gills, this upper surface of the heart receives near the medial 

 line five pairs of vessels (one pair for each segment,) coming 

 from these last organs, and which, according to MM. Audouin 

 and Milne Edwards, are analogous to the branchio-cardiac 

 canals of the decapods. A central canal situated below the 

 liver and intestine, receives the venous blood, which flows in 

 from all parts of the body. At the level of each segment, 

 bearing the fin-feet and gills, it throws out on each side a late- 

 ral branch, repairing to the gill, situated at the base of the 

 corresponding fin-foot. The parietes of these conduits have 

 appeared to the same observers smooth and continuous, but 

 formed rather by a stratum of cellular lamellary tissue, ce- 

 mented to the neighbouring muscles, than by a proper mem- 

 brane. It has seemed to them that these conduits communi- 

 cate together towards the lateral edge of the rings; but of 

 this they are not certain. The afferential or internal vessels 

 of the gills, which in these squillae form plumose tufts, are 

 continued with the hranchio-cardiac canals, are no longer 

 lodged in little cells, pass between the muscles, turn obliquely 

 round the lateral portion of the abdomen, gain the anterior 

 edge of the preceding ring, and proceed to terminate at the 

 upper surface of the heart, near the median line, riding 

 slightly one upon the other. The medullary cordon presents, 

 besides the brain, but ten ganglia, the anterior of which fur- 

 nishes the nerves of the parts of the mouth ; the three fol- 

 lowing those of the six natatory feet, and the last six those of 

 the tail. Thus the last four jaw-feet, although representing 

 the four anterior feet of the decapods, nevertheless form a 

 part of the organs of mastication. The stomach of the same 

 Crustacea (squillae) is small, and presents some very small 

 teeth, towards the pylorus. It is followed by a thin and 



