26 On the present state of Zoology. 
ing to connect the more extreme cases, and thus clearly proving all 
to be of one species. 
From experiencing- the great difficulty which attends the exact dis- 
crimination between species and varieties, especially in certain groups 
in which variation of character is very frequent, some have imagined 
that there was nothing definite or constant in species themselves, but 
that they passed insensibly into one another. To this opinion, al- 
though embraced by many eminent naturalists, we are strongly op. 
posed. It may be true that hitherto no definition of a species has 
been brought forwards which will meet all cases-; but until our means 
of observation shall have been more extended than they have at pre- 
sent, this simply proves the imperfect state of our knowledge on this 
subject. For let us consider how much is wanted to enable us to fix 
such a definition with certainty. It has been observed with reference 
to this point, that " we ought to see species in all their several loca- 
lities from north to south ; to get together all the varieties of age, 
form, colour, and size, in order to construct from all these modifica- 
tions a table representing one well-known species, and to establish as 
many of these tables as there are true species of organized:' beings. 
By these means we should probably arrive at some law which would 
fix the limits of the species in its modifications, and serve consequent- 
ly as the basis of an exact definition."* 
Having brought our remarks to this point, we shall simply, before 
concluding, say a few words for the direction of those, who may be 
entering on the branch of science we are here considering. We have 
more than once alluded to the immense field which Zoology brings 
before us. We have also noticed the great partiality shown by na- 
turalists towards certain parts of that field in preference to others. 
Now what we would recommend to such as really desire to advance 
its progress, is, that they restrict their chief attention to some given 
department, and, when practicable, to those particular groups which 
have been least studied. It is utterly out of our power to become 
acquainted with all the existing species of nature. The longest life, 
added to the enjoyment of the most favourable opportunities, will not 
suffice for acquiring more than a very limited knowledge of the de- 
tails of their history. It must, then, be by division of labour, that 
we try to perfect the science, so far as human researches can perfect 
it. We must bring our observation to bear on those parts of it which 
are behind the others, we must apportion such parts amongst us ac- 
cording to the respective circumstances in which we are placed, and 
* Lam. Hist. Nat. des An. sans Vert. (2d edit.) torn. i. p. 166 Note by the 
Editors. 
