HOW GENERA ARE GENERATED 57 
exasperated to find that there is practically no finality in 
these matters. It is important to remember that this cannot 
be helped, so long as knowledge is in the stage of growth, 
the stage in which it is most acceptable to the human intel- 
lect, by continually holding out the invigorating hope of 
new acquisitions. In the progress of science some animal 
hitherto unknown or little noticed attracts the attention 
of a naturalist. Describing some of its salient features, 
he makes it the typical species of a new genus. In course 
of time many other animals are found to have characters 
almost identical, and they constitute the various species of 
the same genus, till the number of them becomes so large 
that they are perhaps at first grouped in lettered or num- 
bered sections, to which presently names are given as sub- 
genera, and these in turn are raised te the rank of genera, 
and sometimes eventually to higher grades in the system. 
At each successive improvement there comes a displace- 
ment of the old names, and for the accurate designation of 
specimens the unskilled are placed at greater and greater 
disadvantage. There was a time when all the Crustacea 
were included. among insects, but to call a lobster an in- 
sect would now be regarded as a proof of ludicrous igno- 
rance. The existing genus Cancer is an absurd little 
remnant of that which was originally established by 
Linnzeus, and which has been gradually subdivided into 
a long array of genera, and families, and legions, and 
sub-orders, and orders. Bell, in 1853, in his ‘ British 
Stalk-eyed Crustacea, says, ‘There is but one species of 
this genus, as now restricted, native of the shores of this 
country, or indeed of Europe, all the others being South 
American.’ He refers, however, to the species discovered 
by Say, which belong to the East Coast of North America. 
The great eatable crab of our own shores is well known. 
Dr. Leach remarks that ‘at low tide they are often found 
in holes of rocks, in pairs, male and female, and if the 
male be taken away, another will be found in the hole at 
the next recess of the tide. By knowing this fact, an 
experienced fisherman may twice a day take with little 
trouble a vast number of specimens, after having once 
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