as Invertebrate Embryology, very much must necessarily be omitted, 

 but it seemed to us better to run the risk of criticism on this score 

 and to bring our survey of the field to a conclusion within a reason- 

 able period, rather than to attempt to give a complete account of all 

 that is known of Invertebrate Embryology. Such an attempt would 

 involve the task of writing not a single volume but a series of 

 volumes ; it would require for its accomplishment many years and 

 would be beyond the powers of one man. Moreover, the first volume 

 would be out of date long before the last volume was published. 



The literature lists have been purposely kept as brief as possible 

 — as a rule only the most recent papers on the subject have been cited. 

 Where earlier papers have been referred to it is chiefly because these 

 papers, in laying the foundation of our knowledge, have not been 

 superseded by later work. 



In conclusion, my best thanks are due to my colleagues, Professor 

 Lefroy and Mr. Dobell, for valuable suggestions, and to my wife for 

 much help in the tedious work of preparing the Index. 



E. W. M. 



Iiii'EitiAL College oi' Science, South Ken.sinoton, 

 Jidy 29, 1914. 



