296 
HISTORY OF BRITISH CRUSTACEA. 
(and hence the name of the Order, from an oar, and 
7TOU9, a foot). Ovary external. 
Pam. CYCLOP ID M 
Head and body not distinguishable, being consolidated 
with the first segment of the thorax. Two pairs of foot-jaws. 
Five pairs of legs; the fifth pair rudimentary. One eye. 
The male has a swollen hinge-joint to both antennse. The 
various species are found in fresh or salt water. Dr. Baird 
observes, “ The fresh-water species abound in the muddiest, 
most stagnant pools, and in the clearest springs; and the 
ordinary water, with which the inhabitants of London are 
supplied for domestic purposes, often contains them in great 
numbers. The marine species are to be found frequently 
in immense quantities in small pools on the sea-shore, within 
high-water mark, living among the seaweeds and corallines 
which so elegantly fringe the beautiful little wells and clear 
round pools which are hollowed out in the rocks on the 
coast, and are to be met with in equal profusion in the open 
ocean, where, by the curious luminous properties they pos- 
sess, they assist in producing that beautiful phosphorescent 
appearance of the sea, the cause of which formerly puzzled 
naturalists.” J urine has calculated that a single specimen of 
