Mr. J. D. Dana on Zoophytes. 105 



raise it aboye the Polyp. In such cases, the system of structure 

 typical of a group is ascertained by a general study of the spe- 

 cies, and then an acquaintance with this structure assists in 

 tracing out transitions, and determining how far one and another 

 organ may fail without requiring an entire separation of an in- 

 dividual from the group. 



To classify requires therefore the widest possible range of 

 knowledge of organic beings, and the nicest balancing of affini- 

 ties : and we remark again, that it consists rather in expressing the 

 various chains of affinities or homologies direct and parallel, with 

 their shadings and blendings, than in searching for certain in- 

 violable characteristics for distinguishing groups of species. 



Classification of Zoophytes. — In view of the foregoing prin- 

 ciples, any classification of Zoophytes made out without refer- 

 ence to the structure of the animals must necessarily be faulty. 

 There have been several of this kind in the department of Corals ; 

 and as the subject has been little understood till within a few 

 years past, errors were to be expected. They subserved, for 

 the time, the purpose of systematizing the facts known, and 

 afforded a means of characterizing species : so far they were good. 

 But at the present day, to make out a classification based on the 

 corals alone and the easiest method of distinguishing them, 

 would partake of times of past ignorance : they can no more be 

 properly arranged without reference to their animals, than shells 

 without regard to their mollusks. The zoological relations of 

 the species should be first studied, and afterwards such characters 

 laid down for the corals as belong to the orders and families thus 

 deduced. 



The first classification of Zoophytes in which the animals 

 received attention was offered by Blainville*. Lamarck had led 

 the way with a discriminating study of the corals. Blainville 

 availed himself of the observations of Quoy and Gaimard, besides 

 the few investigations of older authors, and with great acumen 

 made out an arrangement, which in its general features was 

 highly natural. He divided Zoophytes, including the Actinia, 

 into the groups Zoantharia, Polypiaria, and Zoophytaria ; and 

 if we strike out from Polypiaria a few species that belong to 

 the first division, and others that are Bryozoa, we have the groups 

 Zoantharia and Zoophytaria corresponding to the groups Actinaria 

 and Alcyonaria of the classification by the writer, and Polypiaria 

 nearly to the Hydroidea. The only other change of importance 

 which the writer has proposed in these primary subdivisions is 



• * Manuel d'Actinologie ou clc Zooph3'tologie, par IT. M. D. dc Blain- 

 ville. 644 pp. 8vo, with an atlas of 100 plates. Pi;ris, 1834. (The 

 printing began in 1 830.) 



Ann. $ Mag. N. Hist. Vol. xx. 8 



