xvi THE HISTORY OF ZOOLOGY 645 



embryological methods began to revolutionise the science. 

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



VERTEBRATA. 



MOLLUSCA. ANNULOSA 



MOLLUSCOIDA [including Arthropoda and Annulata]. 



[including Brachiopoda, Polyzoa and ANXULOIDA 



Tunicata]. 



[including Echinodermata, Rotifera, 

 CCELENTERATA. 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 echinopaBdium. 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 

 conjugation was misinterpreted as a true sexual process, the 

 mega-nucleus being considered as an ovary, the micro-nucleus as 

 a testis. 



Haeckel, apart from his elaborate and beautiful researches 

 on the Radiolaria, Calcareous Sponges, and Hydrozoa, is remark- 

 able 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, coenogenesis and palingenesis, and 

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

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

 form of genealogical trees, and he was the first to employ the 

 method of introducing hypothetical ancestral forms, wherever 

 they might be wanted to complete the connection between known 

 groups. He may be said, in fact, to have founded a school of 

 deductive zoology, the phylogenetic speculations of which are 

 often as ingenious and suggestive as they are transient. The 

 student must, however, bear in mind that Archi-molluscs, Ideal 

 Craniates, and Pro-mammalia are mere figments of the imagina- 

 tion, and have no more real existence than the " Divine Arche- 

 types " of an earlier school of thought. 



One result of the new views on species, very obvious in the 

 writings of both Huxley and Haeckel, was the marked alteration 

 in the position assigned to Man in the animal series. Linnaeus 

 considered jEfcwioasagenus of his order Primates, equivalent to Simia, 

 Lemur, &c. ; but Cuvier took the retrograde step of erecting a 

 distinct order, Bimana, to contain Man alone, the Apes and 



