PREFACE. 



Dr. Baird's work on ' The Natural History of the 

 British Entomostraca,' published by the Hay Society 

 in 1850, marked an important stage in British Natural 

 History research, and forms the basis of the present 

 volume. That work contains a complete account of 

 the Copepoda found living as parasites on British 

 fishes, so far as then known. Much has been done 

 since then to extend our knowledge of these organisms, 

 and many species have been added to the number 

 recorded by Dr. Baird. His work naturally tended to 

 produce such results, for it placed before British 

 students, in a concise manner, a large amount of 

 interesting information concerning these parasitic 

 forms, and, by showing the successful results which 

 had already been accomplished in other countries 

 among such curious animals, led to an increased 

 interest in their study. 



' A Monograph of the Free and Semi-Parasitic 

 Copepoda,' by Dr. Gr. S. Brady, was published by the 

 Ray Society in 1878-1880. That work, which con- 

 sists of three volumes, marked a second important 

 stage in the study of these minute crustaceans, and 

 was an evidence of the increasing attention their study 

 was receiving. But though several groups of the non- 

 freeliving species were described in that Monograph, 

 those found parasitic on fishes were expressly omitted. 

 The author in his Introduction states : " The truly 

 parasitic forms — fish-lice, etc. — are excluded as not 

 coming within the scope of my work. They are of 

 themselves sufficient to occupy an independent volume, 



