34 HENRY B. BRADY. 
arranged alternately in two or three distinct axes, but not 
on a spiral plan. 
Order 7. AGATHISTEGUES.—Shell composed of chambers 
wound round a common axis, each forming half the circum- 
ference ; texture smooth and imperforate. 
Whilst there are certain advantages to be derived from a 
purely artificial arrangement—as, for example, the Linnean 
classification of plants—it is seldom that such a method 
can be adopted without violence in one way or other to 
manifest natural affinities, and the lowest divisions of the 
animal and vegetable kingdoms are perhaps least of all 
suited for its introduction. The chief difficulties that beset 
the student of systematic zoology, when engaged upon these 
low types of animal life, arise from the wide range of mor- 
phological variation he is obliged to admit within the limits 
assigned to species; and although there is a great difference 
in different genera as to the degree of persistence in the dis- 
tinctive characters of their subordinate forms, it may be 
fairly doubted whether “species,” in the sense in which the 
word is rightly applied to animals of more complex organisa- 
tion, can be said to exist amongst the lower Protozoa. It is 
only as we learn to recognise the fact that amongst the Rhi- 
zopoda the so-called ‘‘ species’? represent no more than terms 
of a series of which very frequently every intermediate link 
can be supplied, that we arrive at any just conception of their 
relationship. This being so, it is easy to see where a purely 
artificial classification must inevitably break down; and 
though the d’Orbignian scheme was a fair attempt to deal 
with a great mass of facts, collected by its author with infi- 
nite labour, it has now ceased to be of service, and has fallen 
into desuetude. Its defects are too obvious to need comment ; 
it had none of that elasticity which gives to a system of clas- 
sification the element of permanence, and which can only 
exist in proportion to the degree in which it is based upon 
natural affinity and the natural sequence of forms. 
In the year 1854 Professor Max Schultze published his 
classical memoir, ‘ Ueber den Organismus der Polythalamien 
(Foraminiferen),’ and with it an exposition of his views on 
the classification of the Rhizopoda. His conclusions, sum- 
marised in a convenient table at the end of the volume, are 
briefly as follows. The Rhizopoda are divided primarily into 
Nupa and Tesracka, the former with the genus Ameba for 
its type, the latter embracing all the forms having an external 
shell or other investment. The Txstacea are divided into 
two suborders—WVonothalamia and Polythalamia—the one 
