342 NATURAL SCIENCE. May, 



which, " like the stars, are in different stages of progress and decay. 

 Some, as the Earth and Venus, at least in her Polar Regions, have 

 cooled down sufficiently to be covered by a hard crust, and to be fit 

 abodes for living creatures ; others, like J upiter and his fellow giant 

 planets, are still in a more or less heated and partly self-luminous 

 condition." 



Having, so to say, put the earth in her place, Mr. Clodd proceeds 

 to give a brief review of her geological history and of the fossil record 

 of gradually evolving forms of life. Then with a pleasant lucidity he 

 describes the gradations that exist among the existing forms of 

 animals and plants. 



The second section of his book Mr. Clodd entitles "explanatory." 

 In that, positing matter and force and the unequal distribution of the 

 masses of matter in a first chaos of the universe, he describes the 

 origin of stars and systems, and in particular the origin of our own 

 planetary system. Then he gives a brief review of the evolution of 

 organic life on our own globe, and of the arguments supporting 

 Darwin's principle that Natural Selection is the chief agency in this. 

 All this part is done admirably and clearly, in a fashion that will 

 command the respect of those familiar with the difficulty of presenting 

 so complicated a series of arguments in a compact and coherent form. 



Mr. Clodd has done his work well, and the inquiring reader will 

 find, not indeed an answer to the problem of the universe, but some- 

 thing on which to stay his mind. The acceptance of the principle of 

 evolution as ruling all the changes of matter and force, whether they 

 be displayed in the great masses of stellar space or in the surging 

 changes of the atoms and molecules of organic matter, merely pushes 

 back the " why " of things to a further place. But the grandeur and 

 the universality of the " explanation " afforded by evolution may 

 narcotise many minds into peace ; and w r hen there are no ultimate 

 explanations one narcotic is as good as another. 



Dr. Hertwig's Text-Book of Zoology. 



Lehrbuch der Zoologie. By Dr. Richard Hertwig. Third improved edition. 

 Pp. 600, many illustrations. Jena: Gustaf Fischer, 1895. Price 11 marks 

 50 pf. 



The third edition of Dr. Hertwig's text-book has been carefully 

 revised, and a considerable amount of new material introduced. 

 The account of the Porifera has been much modified, a very large 

 addition to our knowledge of this group having been made since the 

 earlier edition appeared. The Lamellibranchs, too, appear in an 

 altered form, as recent work of Neumayr, Pelseneer, Jackson, 

 Grobben, and others make our former views untenable. The 

 palaeontological side has been slightly extended, but it still remains 

 the weakest side of the book. In many respects we regard Dr. 

 Hertwig's text-book as considerably in advance of other books in 

 English, German, or French, and we think it the more to be 

 regretted that due importance is not given to extinct forms. The 

 divorce between palaeontology and zoology, so lamentable in museums, 

 is even more lamentable in text-books. Where the zoologist ven- 

 tures upon palaeontology he is always insufficient, and not infrequently 

 erroneous. Where the palaeontologist ventures upon zoology, so far 

 as we have had opportunity of judging, he is almost invariably 

 ludicrous. A true text-book of zoology remains to be written ; but 

 of those in existence Dr. Hertwig's, in lucidity and correctness, is 

 probably the first, certainly among the first three. 



