X PREFACE 



to photograph for us the zoning of algae reproduced on 

 Plate VIII ; and Mr. E. L. Gill, the curator of the Hancock 

 Museum, Newcastle-on-Tyne, rendered us a similar service 

 in connection with a fine specimen of a sea-lily in the 

 collection under his charge. We are especially indebted to 

 Mr. G. P. Dufifus of the Natural History Department, 

 Marischal College, University of Aberdeen, for much 

 assistance with the work of photography in general. The 

 source of one or two borrowed line-drawings is acknowledged 

 in the text. Figures 5-9, 17, 18, 20 and 21 were drawn by 

 Miss Mary Mackenzie, while Nos. 14 and 15 are the work 

 of Miss Alice Davidson. 



In conclusion, we have great pleasure in thanking the 

 publishers, Messrs. Sidgwick and Jackson, for the courtesy 

 with which they have listened to our suggestions and the 

 pains they have taken to give them effect. 



