ORDER STOMAPGDA. 
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 affierential or internal vessels 
of the gills, which in these squillm form plumose tufts, are 
continued with the brancltio-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 (squilloe) is small, and presents some very small 
teeth, towards the pylorus. It is followed by a thin and 
