1897] SOME NEW BOOKS 201 
the concrete examples of the practical text-book. It is, however, 
only to a limited extent that such co-operation is possible or prac- 
ticable. The number of types which can be described within the 
limits of a practical text-book must be necessarily few by comparison 
with the ground covered by the more abstract treatises, and illustra- 
tive only of the greater systematic divisions. The design of our 
authors is an ambitious one. It is nothing less than to effect a com- 
promise, so to speak, between the abstract and the particular, and to 
impart a general knowledge founded upon judiciously constructed, 
concrete examples. 
A complete knowledge of a natural group of animals might be 
supposed attainable only by a separate description of each of the 
species in it. But allied species and even genera only differ amongst 
themselves by secondary characters, and it is not until we come to 
families or orders that we find anatomical characters of sufficient 
importance to warrant detailed treatment in the limited compass of a 
text-book. Hence for each such systematic division the authors pro- 
pose to commence with the description of a generalised type, in which 
the characters of the subgroup—in most cases a suborder—shall be 
found combined, and then to proceed to point out how the various 
forms comprised in the subgroup differ severally from the essential 
type. But such generalised and fundamental types are to be found 
but rarely in nature. The authors have therefore invented and con- 
structed a morphological type for each suborder, a fundamental 
form “which summarises in itself that which is common to all the 
actual forms of the group, or which is presented as a simple initial 
form, from which the others would be derived by progressive com- 
plications.” In this way it is possible to present general notions in a 
concrete form. It might be objected that the morphological types 
are not real but represent to a certain extent ideal abstractions, In 
answer to this it is pointed out that the term concrete does not 
mean real. “A type may be concrete even though it is ideal 
What does it matter to a student when he reads a precise description 
with the indication of all the organs and of their relations, whether 
the being thus described really exists in nature or whether it repre- 
sents only the mean, we might almost say the composite portrait, 
of a small group of real beings? The idea he will obtain of the being 
described, and later of the entire group, will be none the less precise 
and none the less accurate.” 
For the reasons that have just been set forth, Messrs Delage and 
Hérouard call their work a treatise of concrete zoology, as opposed 
to the more abstract zoology of the ordinary text-books. They 
claim, and we think justly, to have helped the student over one of his 
greatest difficulties, though as they acknowledge, the Protozoa are 
scarcely a fair test for the efficiency of the method on account of their 
simple structure, and we are begged to suspend our final judgment 
until the appearance of the volumes to follow. At the same time the 
great store of information brought together in a most painstaking and 
laborious manner renders the work very useful to others than 
beginners, chiefly on account of the simple and methodical arrange- 
ment that has been adopted, and the consequent ease with which any 
required facts can be hunted down. 
