246 LEADING AMERICAN MEN OF SCIENCE 



was 483, of which 229 were new. The Zoophytes were divided 

 into the two orders, Actinoidea and Hydroidea; and the former of 

 these orders was divided into the two suborders, Actinaria and 

 Alcyonaria. The order Actinoidea, as denned by Dana, is equiva- 

 lent to the class Anthozoa, or Actinozoa, as generally recognized by 

 zoologists to-day; and his two suborders of Actinoidea exactly rep- 

 resent the two orders into which most naturalists would divide the 

 class to-day. In Dana's work, then, was published for the first time 

 a classification involving both a correct delimitation of the group of 

 Anthozoa (sea-anemones and coral animals), and a true discrimi- 

 nation of its two main divisions. The advance of knowledge in the 

 last half-century has made important changes in the details of the 

 classification, but in its broad outlines Dana's classification has 

 stood the test of time. 



The study of the Crustacea was in a more advanced state than 

 that of the corals before Dana's work. There was no occasion, 

 therefore, for a revision of the whole group in his Report on the 

 Crustacea. It is, however, a striking proof of the diligence with 

 which the work of collecting was prosecuted under manifold dif- 

 ficulties that he catalogues six hundred and eighty species col- 

 lected in the Expedition, of which over five hundred were new. 



The study of this group of animals suggested to Dana a striking 

 generalization, which was first enunciated in the Report on Crus- 

 tacea, but which was later discussed more fully in a number of 

 papers, most of which were published in the Journal of Science 

 (1863-66) the principle of cephalization. 



In the Crustacea, as in the Arthropoda in general, each seg- 

 ment of the many-jointed body bears typically a pair of jointed 

 appendages, which are serially homologous, though appropriated 

 to different functions. In the highest Crustacea, as the crabs 

 and lobsters (Decapoda), the eight anterior segments bear append- 

 ages cephalic (i. e., sensory or oral) in function; namely, two pairs 

 of antennae, one pair of mandibles, two pairs of maxillae, and three 

 pairs of accessary mouth-organs (maxillipeds) ; while the next 

 five segments bear the principal locomotive appendages. In a 

 lower group represented by the sow-bugs and sand-fleas (Arthros- 



