BRYOZOA. 289 



powers of discrimination and observation. To Dr. H. A. Nichol- 

 son the student of Palaeozoic TREPOSTOMATA is more indebted 

 than to any other naturalist, since to him belongs the credit of 

 being the first to recognize the absolute necessity of thin sec- 

 tions. His works mark a new departure, an epoch in the study 

 of these intricate fossils, and it is upon the outlined basis first 

 drawn by this brilliant naturalist, that my own work has been 

 built. We agree admirably upon fundamental principles and 

 the facts involved, and if we differ more or less in our conclu- 

 sions, I think it is mainly because Dr. Nicholson has not gone 

 into the comparative anatomy of the subject as deeply as I 

 have found it necessary to do. Nor can he have had any ade- 

 quate idea of the vast variety and number of the forms under 

 consideration. 



To enhance the value of my work I have extended my inves- 

 tigations so as to embrace not only Palaeozoic, but also all 

 available Secondary, Tertiary, and recent material. The ex- 

 haustive works of D'Orbigny, Busk, Reuss, Manzoni, Hagenow, 

 Hincks and other authorities on the subject, were carefully 

 studied and searched for information which might throw some 

 light upon the early representatives of the class here treated. 

 Much success has attended my endeavors in this direction and 

 the classification now offered, though essentially the same as 

 the scheme published in my "American Palaeozoic Bryozoa," is 

 nevertheless much improved and more natural, as the whole is 

 based upon the microscopic and really fundamental characters 

 of the organisms. Nearly four thousand thin sections were 

 prepared, illustrating the internal characters of between six 

 and seven hundred species. 



It is not claimed that the system adopted applies correctly in 

 all cases, but I am convinced that the outlines as herein drawn 

 will recommend themselves to all who will undertake the study 

 of the Palaeozoic Bryozoa with an unprejudiced mind and a firm 

 determination to master them. Such a student will quickly 

 learn that, as soon as he has accustomed himself to taking 

 note of every variation, and grasped the fundamental principles 

 of the system, the subject is less difficult than it at first seemed, 

 as he will find that his specimens usually drop naturally enough 

 36 



