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 to 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 

 Linnaeus, 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 clay take with little 

 trouble a vast number of specimens, after having once 



