vi ZOOLOGY 
These facts have led me to treat the subject largely 
from a morphological standpoint, touching but lightly on the 
Histology, Embryology, and Natural History of the forms 
described. More space has been, as a rule, devoted to those 
animals which are regarded as intermediate between the larger 
groups than to the more specialised members of the groups. 
Any system of classification is to some extent a matter of 
personal judgment. I do not suppose that adopted here has 
any finality, but I hope the tables given will be of use to the 
student as expressing the results of the most recent research. 
In preparing the volume I have been much helped by 
numerous friends, to whom my best thanks are due. Dr. 
D. Sharp, Dr. Hickson, Mr. Beddard, Mr. J. J. Lister, Mr. 
F. G. Sinclair, Mr. C. Warburton, and Mr. MacBride, have all 
given me the most generous assistance, and, above all, I am 
most deeply indebted to my friend Mr. 8. F. Harmer, who has 
in the most kind way read through the proof-sheets, and whose 
careful revision has saved me from many errors. 
To the Delegates of the Clarendon Press I owe thanks 
for permission to use Fig. 133, taken from Rolleston and 
Jackson’s Forms of Animal Life. Uerr Fischer of Cassel has 
kindly given me leave to use some reductions from the admir- 
able diagrams of Professor Leuckart; these occur in the 
groups Echinodermata and Arthropoda, and are acknowledged 
under each eut; similarly the firm of Wieweg and Son have been 
good enough to allow me to use four figures taken from Vogt 
and Yune’s Lehrbuch der Praktischen Vergleichenden Anatomie. 
I am also indebted to Messrs. Macmillan and Co. for their 
kindness in allowing me to use Figs. 37, 89, and 90, all of 
them taken from Professor Parker’s Hlementary Biology. 
ARTHUR E. SHIPLEY. 
Curist’s CoLLEGr, CAMBRIDGE, 
March 1893. 
