NATURAL HISTOKY — ZOOLOGY. 213 



were imperfectly understood, and, as a consequence, many groups of 

 animals had been temporarily located in a false position, such as bats 

 and whales by the ancients, and the Polyzoa and Foraminifera in 

 more modern times. These resemblances in form were illustrated 

 generally by the classes of Vertebrata, and more especially by the 

 various orders of Mammalia — the Invertebrata affording, however, 

 many remarkable examples. Since no principle of gradation of form 

 would sufficiently account for these analogies, the author had endea- 

 voured to discover some other explanation, and had come to the 

 conclusion, that the fact of deviations from typical form being 

 accompanied by modifications of typical habits, afforded the desired 

 clue. Examples of this were given, and the principle educed, that 

 agreement of habit and economy in widely-separated groups is 

 accompanied by similarity of form. This position was argued 

 through simple cases to the more complex, and the conclusion 

 arrived at, that where habits were known, the explanation sufficed ; 

 and it was only in the case of animals of low organization and 

 obscure or unknown habits, that any serious difficulty arose in its 

 application, so that our appreciation of the rationale of their simi- 

 larity of form was in direct ratio to our knowledge of their habits 

 and modes of life. In conclusion, by a comparison of the Polyzoa 

 with the Polyps, it was shown that the economy of both was nearly 

 identical, although they possessed scarcely anything in common 

 except superficial characters, and this identity of habit was regarded 

 as the explanation of their remarkable similarity of form. 



PERSISTENT TYPES OF ANIMAL LIFE. 



A DISCOURSE on this subject has been delivered at the Royal 

 Institution, by Professor Huxley. He reminded his audience of what 

 is meant by geological time, the forms of animal and vegetable life 

 found in the lowest strata or layers of the earth's crust being consi- 

 dered to be earliest created. He stated that it was the growing 

 conviction of geologists that the remarkable changes in the earth's 

 crust are not due to violent rapid action, as supposed by early ob- 

 servers, but rather to the efficacy of gentle forces operating through 

 very long periods of time, as seen now in the slow-floating ice of 

 glaciers and the slow-growing coral reefs. He also considered that 

 paleontologists had greatly exaggerated the number of animals viewed 

 as extinct. After long investigation he concluded that of 120 ordinal 

 types of animals only eight or nine types were extinct ; and he 

 added, on the authority of Dr. Joseph Hooker, the eminent botanist, 

 that of the 200 ordinal types of plants not one was wanting. Pro- 

 fessor Huxley exemplified his views from all departments of the 

 animal kingdom — from the Polyzoa up to the Vertebrata — specimens 

 of each being found in very low strata. He did not, therefore, 

 believe that there was much greater difference between the earth's 

 appearance in early geological times, and in our own, than there is 

 now between the different regions of the globe. He remarked, in 

 conclusion, that the little change in the persistent types of animal 

 and vegetable life appeared to him to "indicate that each is but the 



