224 ESSAY ON CLASSIFICATION 



Cl. 24. Acalephae. 



Cl. 25. Anthozoa. 



Cl. 26. Trematodea. (Entozoa with ramified intestine, also Cercaria.) 



Cl. 27. Complanata. (Dendrocoela: Planaria, etc.) 



Cl. 28. Polygastrica. 



The system of Zoology published by Ehrenberg in 1836 presents 

 many new views in almost all its peculiarities. The most striking of 

 its features is the principle laid down that the type of development 

 of animals is one and the same from Man to the Monad, implying 

 a complete negation of the principle advocated by Cuvier, that the 

 four primary divisions of the animal kingdom are characterized by 

 different plans of structure. It is very natural that Ehrenberg, after 

 having illustrated so fully and so beautifully as he did the natural 

 history of so many organized beings, which up to the publication of 

 his investigations were generally considered as entirely homogeneous, 

 after having shown how highly organized and complicated the in- 

 ternal structure of many of them is, after having proved the fallacy 

 of the prevailing opinions respecting their origin, should have been 

 led to the conviction that there is, after all, no essential difference 

 between these animals, which were then regarded as the lowest, and 

 those which were placed at the head of the animal creation. The in- 

 vestigator who had just revealed to the astonished scientific world 

 the complicated systems of organs which can be traced in the body 

 of microscopically small Rotifera must have been led irresistibly to 

 the conclusion that all animals are equally perfect, and have assumed, 

 as a natural consequence of the evidence he had obtained, that they 

 stand on the same level with one another, as far as the complication 

 of their structure is concerned. Yet the diagram of his own system 

 shows that he himself could not resist the internal evidence of their 

 unequal structural endowment. Like all other naturalists, he places 

 Mankind at one end of the animal kingdom and such types as have 

 always been considered as low at the other end. 



Man constitutes, in his opinion, an independent cycle, that of na- 

 tions, in contradistinction to the cycle of animals, which he divides 

 into Myeloneura, those with nervous marrow (the Vertebrata) and 

 Ganglioneura, those with ganglia (the Invertebrata). The Verte- 

 brata he subdivides into Nutrientia, those which take care of their 

 young, and Orphanozoa, those which take no care of their young, 

 though this is not strictly true, as there are many Fishes and Reptiles 



