x PREFACE: 
applicable to a few genera only, which are considered 
as its type, and does not embrace other genera which 
are regarded as belonging to it, but beginning to as- 
sume the characters of some of the other neighbour- 
ing groups. There is here the use of a method, 
where there is no precision, and a boasting that the 
plan of Nature is followed, when that plan is con- 
fessedly incomprehensible. Indeed, it often hap- 
pens, that the admired natural method of one zoo- 
logist differs from the censured artificial method of 
another, merely in the circumstance that different 
systems of organs have been made choice of as the 
basis of the respective classifications. Unless zoo- 
logists, in the formation of their primary groups, 
endeavour to determine those characters which all 
the members possess in common, admitting only such 
marks into the definition, and practise the same me- 
thod with all the subordinate divisions, the progress 
of the science will be unsteady, the student will be 
startled at its contradictions, and the revolutions in 
nomenclature become as frequent as the cultivators 
of the science are numerous. 
The ridicule too often thrown out against 
some of the departments of Zoology, by persons who 
pretend to considerable intellectual acquirements, 
