PREFACE ix 



ner, as a graduated course of instruction, and to consider 

 the effect upon the entire scheme of using a term of funda- 

 mental importance in two utterly different senses. 



A large proportion of the figures are copied either from 

 original sources or from my own drawings the latter when 

 no authority is mentioned. The majority, even of those 

 which have previously appeared in text-books, have been 

 specially engraved for the work, the draughtsman being 

 my brother, Mr. M. P. Parker. In order to facilitate 

 reference the illustrations referring to each subject have, as 

 far as possible, been grouped together, so that the actual is 

 considerably larger than the nominal number of figures. 

 Full descriptions are given instead of mere lists of reference- 

 letters : these will, I hope, be found useful as abstracts of 

 the subjects illustrated. 



I have to thank my friends Mr. A. Dillon Bell and Pro- 

 fessor J. H. Scott, M.D., for constant and valuable help in 

 criticising the manuscript. To Dr. Paul Meyer, of the 

 Zoological Station, Naples, I am indebted for specimens 

 of Polygordius ; and to Professer Sale, of this University, 

 Professor Haswell, of Sydney, Professor Thomas, of Auck- 

 land, and Professors Howes and D. H. Scott, of South 

 Kensington, for important information and criticism on 

 special points. My brother, Professor W. Newton Parker, 

 has kindly promised to undertake a final revision for the 

 press. 



D UNEDIN , N.2., 



8 9 0. 



