PREFACE 



The present volume contains an account of a few types selected 

 from the chief groups of the animal kingdom, followed and 

 accompanied by a consideration of some of the more general 

 conclusions of biology. It is inevitable in an elementary hand- 

 book to use the type system, but it is not necessary to use it in 

 such a way as to emphasize all the faults of the system. The 

 gravest fault, in my opinion, is that the student is impressed 

 with the idea that the characters of a given species selected for 

 description are distinctive of a wider assemblage of forms. I 

 have endeavoured to obviate this by emphasizing here and 

 there the differences between allied forms. Many distinguished 

 authorities hold that in treating of animal structure it is desirable 

 to commence with the higher forms and gradually work down 

 to the lower forms. It is argued that to do this is advantageous, 

 since the student commences with what must be the more 

 familiar part of the subject. Some rough notion of human 

 anatomy is possessed by most persons ; whereas the very 

 methods by which the lower animals are studied are new to the 

 beginner. There is, however, no transition between a dissection 

 of a frog with scalpel and scissors and the examination of an 

 amoeba with the microscope. The plunge into an unfamiliar 

 region of the subject must be made some time ; and why not 

 at the very commencement ? Besides, to begin with the low 

 forms and to gradually work to the higher has the undoubted 

 advantage of presenting the facts in a logical sequence. 



I therefore begin with the amoeba, and deal with the other 

 types in, so far as is possible, an ascending order. 



