134 MODERN IDEAS OF EVOLUTION 



strengthen the argument from analogy ; and un 

 doubtedly there are many groups of closely allied 

 species, or of races confounded with true specific 

 types, which it might not be unreasonable to suppose 

 of common origin. These are, however, scattered 

 widely apart, and the contrary fact of extensive gaps 

 in the scries is so frequent that Haeckel is constantly 

 under the necessity of supposing that multitudes of 

 species and even of larger groups have perished, just 

 where it is most important to his conclusion that they 

 should have remained. This is of course unfortunate 

 for the theory, but then, as Haeckel often remarks, 

 &amp;lt; we must suppose that the missing links once existed. 

 But thirdly, these gaps which now unhappily exist 

 may be filled up by fossil animals ; and if in the suc 

 cessive geological periods we could trace the actual 

 phylogeny of even a few groups of living creatures, 

 we might have the demonstration desired. But here 

 again the gaps are so frequent and serious that 

 Haeckel scarcely attempts to use this argument further 

 than by giving a short and somewhat imperfect sum 

 mary of the geological succession in the beginning of 

 his second volume. In this he attempts to give 

 a series of the ancestors of man as developed in 

 geological time ; but of twenty-one groups which he 

 arranges in order from the beginning of the Lauren- 

 tian to the Modern period, at least ten are not known 

 at all as fossils, and others do not belong, so far as 

 known, to the ages to which he assigns them. This 



