INTRODUCTORY NOTE TO THE ZOOPHYTA. 
Wirutw the past six or seven years the Zoophytes have received more 
attention from naturalists than any other division of the animal kingdom. 
The labors of many, if not most of our ablest naturalists, have been 
directed towards an investigation of the humblest forms of animal life. 
This fact, combined with the recent improved methods and means for 
research, would alone be prophetic of the most signal advances in this 
group ; indeed, our knowledge of all these forms has been so modified, as 
well as increased, that previous writings need rather to be re-written than 
revised. Dana, Agassiz, Milne Edwards, Forbes, Dalyell, Miller, Busch, 
and others, not to mention the continued labors of older observers, have 
effected these changes in this group. 
The work of Dana is most excellent, and will remain a standard of au- 
thority in this department for a long time to come. Aside from the many 
details of structure, in it may be found the first and best philosophical 
exposition of the relations of organic development with these lower plant- 
like forms, Had this work been better known in Europe, there would have 
been saved the constant repetition of the most grave errors. On the labors 
of Agassiz no comment need be made; those who are in this department, 
whether as minute Anatomists or philosophical Zoologists, will not fail to 
understand and appreciate him. In the same field is Busch, who was 
extended his brief though excellent labors over the three classes of this 
whole group; as for the remaining authors mentioned, excepting Midler, 
their position in this department has long been established. Muiller’s 
researches have been mostly on the Hchinoderms, and the careful tracing 
of the phases of their development and metamorphoses; but where so much 
has been done, I fear the limits of this book will preclude full details with 
this class. 
This note would be unnecessary, were it not to show that I do not ignore 
the changes and advance which have been made in this group within the 
past few years; and more especially so, as I have allowed, in this edition, 
the classification to stand as in the original. Any great changes of this 
