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of his work, pointing out some objections wkich may be raised 
against some of his conclusions. 
One of the most prominent features of the work of Professor 
Jack son is the combined study of recent and fossil forms, and 
of .both young and grown stages. It ought not to be necessary to 
point out, that this is really the only way to reach a full under- 
standing of the interrelations of the different groups of Echini; 
scarcely anybody would deny that. But in realitv some echinologists 
study the fossil forms, others the recent — perhaps not because 
they regard their own specialty as the most important, but because 
it is mostly connected with almost insuperable difficulties to procure 
material for the study of both. Prof. Jack son has overcome all 
difficulties. With an energy that demands the highest admiration 
he has got together a material of some recent forms so extra- 
ordinary, that scarcely any Museum-collection can compete with him. 
Thus he has brought together no less than 33,000 specimens of 
Strongylocentrotus drøbachiensis, 2,643 specimens of Toxopneustes 
atlanticus, 1,163 of Paracentrotus lividus, 754 of Echinometra 
lucunter etc., — and every single specimen has been carefully 
examined and tabulated. On the other hånd he has studied a 
very large part of the material of Palæozoic Echini existing in 
both American and European collections. No wonder that he has 
reached results of unusual interest and importance. 
Of course other echinologists also have taken both fossil and 
recent forms into consideration; I might name e. g. Desor, Dun c an, 
Lambert, H. L. Clark and Doderlein, and I also venture to think 
that I have myself not disregarded the fossil forms in my efforts 
to reach a natural classification of the Echini. But Jackson by 
far surpasses all in this regard. Still I might venture to say that 
it is evident that Jackson is first a specialist in the fossil forms. 
It is felt more than once on reading his work, that his knowledge of 
the recent Echinoids is not quite comprehensive, and his conclusions 
are sometimes influenced thereby. It is a faet that specialists on 
fossil Echini are often ineliued to regard only such characters as 
