154 THE ZOOLOGIST. 
most insignificant of animals leads us, step by step, from every- 
day knowledge to the widest generalizations and the most difficult 
problems of Zoology, and indeed of biological science in general.” 
The work, then, although entitled ‘ An Introduction to the Study 
of Zoology,’ is to be regarded not so much as a graphic and 
popularly written exposition of the leading outlines of biological 
science, as a hand-book for those who are desirous, “ crayfish in 
hand,” of gaining for themselves a practical acquaintance with 
the subject from personal observation and experiment. 
After some preliminary remarks on the relation of “ common 
knowledge’’ to science, and a discussion of the derivation of the 
term “ crayfish,” Professor Huxley, in his introductory chapter, 
sets before the reader such points in the structure, growth and 
development of the animal as may be gathered by anyone possessed 
of ordinary powers of observation, and without having recourse to 
special appliances and means of investigation. 
In the two following chapters the physiology of the Crayfish—- 
in other words, the working of the mechanism of its digestive, 
respiratory and circulatory organs, of its muscular and nervous 
systems, and the various organs of sense and reproduction—is 
described; and here, as in the succeeding chapters devoted to 
the consideration of the Crayfish from a purely morphological 
point of view, a multitude of details which to the unscientific 
reader might have become, under less able treatment, wearisome 
and perplexing, are rendered interesting by the author’s graphic 
style and skilful use of illustration, relieved by occasional digres- 
sion on such topics as the nature of the Crayfish-mind,—that 
is to say, the question of its possession of consciousness 18 
discussed, and the extent to which its sensations of light and 
darkness, form and colour, are comparable to those of animals 
higher in the scale of organization and possessed of more highly 
specialized organs of sense. 
Proceeding next to the consideration of the morphology, 
or structure of the various parts and tissues, of the individual 
Crayfish, the composition of the exoskeleton and of the several 
body-rings or “somites” of which it is made up, and of their 
respective appendages is described, and it is shown how all are 
constructed on the same fundamental plan; the nature of the 
epithelium and of the connective muscular and nervous tissues 
is explained; finally, the development of the embryo from the 
ie A a 
