vi PREFACE. 
edition, similar in plan to the first but greatly different in 
its contents, was almost entirely re-written. This edition 
has, like the first, been published in parts between the 
years 1846 and 1855, inclusive. From the high terms in 
which it has already been alluded to from time to time, 
in the writings of various active cultivators of different 
departments of Zoology on the continent, it is obvious 
that the general estimation of his work will still be such 
as might be expected in the case of an author of vast 
erudition, of appropriate tastes, talents and genius, and 
whose office it has been for nearly thirty years, as Pro- 
fessor of Zoology in the University of Leyden, to bring 
the value and import of the new acquisitions of Ana- 
tomy and Zoology (many of them the result of his own 
labours) from time to time before his auditors. 
The University of Cambridge, a few years ago, directed 
in a more marked manner the attention of our students to 
the Moral and Natural Sciences, by proposing honorary 
distinctions to those who might excel in certain depart- 
ments of those sciences respectively; and by requiring 
proof of satisfactory attention to some one at least of such 
departments on the part of all candidates for the degree 
of Bachelor of Arts, who were not aspirants for Mathe- 
matical honours. Amongst the departments of Natural 
Science, Comparative Anatomy and Physiology were 
indicated, with special regard (as is presumed) to Zoology. 
It thus became a part of my office to place within reach 
