XVI THE HISTORY OF ZOOLOGY 685 



Flower in England, and Browne Goode in America, special 

 collections are formed for study and research, while the cases 

 accessible to the public are gradually becoming a series of actual 

 illustrations of zoological science, in which not only the principles 

 of classification, but the chief facts of structure, life-history, and 

 habit are strikingly and adequately shown. Such reforms in the 

 arrangement of museums and the advancement of their usefulness 

 in many directions have been the objects aimed at by the Museums 

 Association, an organisation of those interested in museums in 

 all parts of the world, founded in 1889, 



During the second half of the last century, Zoology as a 

 whole has been greatly influenced by the writings of Thomas 

 Henry Huxley and of Ernst Haeckel. Huxley (1825-1895) 

 was the first to point out the homology of the ectoderm and 

 endoderm of Ccelenterates with the two primary germ -layers of the 

 vertebrate embryo. He also introduced the word zooid, demolished 

 the vertebral theory of the skull, and placed the anatomy of the 

 fossil Ganoids upon a satisfactory footing, as well as making many 

 other important contributions to animal morphology. His Elements 

 of Comparative Anatomy (1864) forms an important landmark in 

 the history of modern Zoology, as giving the views of one of the 

 keenest, most logical, and least speculative of biologists just 

 before the time when the various improved histological and 

 embiyological methods began 1o revolutionise the science. 

 Huxley's " eight primary categories or groups " are as follow : — 



VERTEBRATA. 

 MOLLUSCA. ANNULOSA 



MOLLUSCOIDA [including Artliropoda and Annulata]. 



[including Braohiopoda, Polyzoa and ANNULOIUA 



Tunioata]. [including Bchinodermata, Rotifera, 



C(ELENTERATA. Platyhelminthea and Nemathelminthes]. 



INFUSORIA 

 [including Infusoria proper and 

 Mastigophora]. 

 PROTOZOA 

 [including Rhizopoda, Sporozoa, and Porifera]. 



The lower " Worms '' are associated with Echiaoderms, on 

 account of the resemblance of the adult Rotifers, as well as of 

 the larvae of certain Flat Worms, to the echinopaedium. Sponges 

 are placed among the Protozoa, in accordance with the view 

 that they are to be looked upon as colonies of unicellular zooids. 

 Infusoria are separated from the remaining Protozoa, because 

 the conjugation observed in them was misinterpreted, the 

 meganucleus being considered as an ovary, the micronucleus as 

 a testis. 



Haeckel, apart from his elaborate and beautiful researches on 

 the Radiolaria, Calcareous Sponges, and Hydrozoa, is remarkable 

 as the first modern zoologist to attempt the classification of 



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