KEEPING DARK 815 
formed by Latreille from the Greek words icos, equal, and 
mous, a foot, but, so far from the legs being all alike or 
equal as the name would imply, these appendages often 
have two or three very different developments in a single 
animal. ‘Tiere is, to be sure, a typical form of limb which 
prevails very widely, but the exceptional forms are nume- 
rous and remarkable. With these Latreille was unac- 
quainted, and therefore naturally gives no clue to them in 
the name Isopoda, which he himself interprets as signifying 
‘tous les pieds simples et uniquement propres 4 la locomo- 
tion ou ala préhension.’ In proportion to their importance 
in the economy of the world the Isopoda have hitherto 
attracted little of popular notice. They enjoy still less of 
popular favour. ‘Lhey are all of retiring habits, never 
needlessly courting attention, but in general clinging as 
closely as possible to whatever shelter or holdfast they 
have adopted. Amidst enormous disparities of size and 
strength and shape and temper, this prudent love of ob- 
scurity, the one feature of the moral character which all of 
them possess In common, is strong evidence that all of 
them must have sprung from a common origin. They 
have never tempted mankind to search for them as food. 
The services which they doubtless often render as effective 
scavengers are in some measure counterbalanced by the 
damage which some of them inflict on submarine structures 
and the depredations committed by others on the fruits 
of the garden. Several of the species treat their fellow- 
inhabitants of the sea with little ceremony, and make up for 
smallness of size by ferocity of behaviour. It is only to be 
hoped, as indeed it may be considered certain, that their 
living victims are immeasurably less sensitive to pain than 
ourselves. 
Normally the members of this sub-order have anelongate 
ventrally flattened body, divided into a head of six seg- 
ments under a carapace, a trunk or perzon of seven arti- 
culated segments, and a pleon usually limited to six 
segments. As in all the Edriophthalma, there is no ap- 
preciable ocular segment. ‘The carapace is occasionally 
in coalescence with one or two of the segments of the 
