GrevillEj on the genus Auliscus. 
39 
3 fewer than Babington^ and 20 more than Bentham ! Well 
may the humble student fall back upon the old proverb^ 
Who shall decide when doctors disagree On the one 
side is a war-cry against too many species ; on the other an 
alleged tendency in the opposite direction. " The time may 
ere long arrive/^ says Professor Walker- Arnott^ when what 
are now called genera or subgenera will alone be considered 
species, and another Linnaeus be requisite to reduce the 
chaos to order/^^ 
If such difficulties beset the botanist among the higher 
orders of vegetation^ we need not be surprised to find them 
multiplied when we descend to the more obscure and simple 
forms of organized life. Dr. Carpenter has been unable to 
discover anything approaching to fixity of species among the 
Foraminifera. " The impracticability/^ he remarks, ^' of ap- 
plying the ordinary method of definition to the genera of 
Foraminifera becomes an absolute impossibility in regard to 
species. For whether or not there really exist in this group 
generic assemblages capable of being strictly limited by well- 
marked boundaries, it may be affirmed with certainty that, 
among the forms of which such assemblages are composed, 
it is the exception, not the rule, to find one which is so 
isolated from the rest by any constant and definite peculiarity, 
as to have the least claim to rank as a natural species.^^f 
The Biatomacece, while not, perhaps, in quite so hopeless a 
predicament, are in a very unsatisfactory state, notwithstand- 
ing the labours of Ehrenberg, Kiitzing, Smith, Ralfs, and 
others. With regard especially to the determination of 
species and limits of variation the greatest uncertainty pre- 
vails. A few years ago I remarked in another place — " In 
the present state of our knowledge it would appear that 
scarcely any one character taken by itself is to be relied on, 
and that even a combination of characters which may be 
sufficient for the determination of species in one genus may 
be unsatisfactory in another ; and where groups or sections 
happen to be what is called exceedingly natural, the difficulty 
is greatly increased. Indeed, it often becomes a question 
whether it is best to leave a doubtful variety to embarrass 
the diagnosis, or to separate it under a provisional character. 
No law can be laid down on this subject which shall prac- 
tically be a clear and unerring guide. Among the DiatomacecSj 
the process of self- division, by means of which any deviation 
from the normal condition of a species becomes stereotyped 
and perpetuated with inconceivable rapidity, complicates the 
* ' Brit. Elora/ " Introduction." 
f ' Introduction to the Study of the Foramiinfera,^ p. 56. 
VOL. XI. d 
