664 ZOOLOGY SECT. 



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 Coelenterates 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 

 embryological methods began to revolutionise the science. 

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



VERTEBRATA. 



MOLLUSCA. . ANNULOSA 



MOLLUSCOIDA [including Arthropoda and Annulata]. 



[including Brachiopoda, Polyzoa and ANNULOIDA 



Tunicata]. [including Echinodermata, Rotifera, 



CCBLENTERATA. Platyhelminthes and Nemathelminthes]. 



INFUSORIA 

 [including Infusoria proper and 



Mastigophora]. 

 PROTOZOA 



[including Rhizopoda, Sporozoa, and Porifera]. 



The lower " Worms " are associated with Echinoderms, 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 mega- 

 nucleus 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 

 animals on a frankly evolutionary basis. We owe to him the 

 terms phylogeny and ontogeny, caenogenesis and palingenesis, and 

 the fruitful " gastraea-theory," according to which the gastrula is 

 the ancestral form of all the Metazoa. His classifications take the 



