616 THE BEGINNINGS OF LIFE. 



Silurian epoch are wonderfully like the millepores of 

 our own seas, as every one may convince himself who 

 compares Heliolitis and Heliopora. . . . Turning to the 

 Mollusca, the genera Crania, Discnia, and Lingula have 

 persisted from the Silurian epoch to the present day 

 with so little change that competent malacologists are 

 sometimes puzzled to distinguish the ancient from the 

 modern species. Nautili have a like range, and the 

 shell of the liassic Loligo is similar to that of the 

 " squid " of our own seas. Among the Annulosa^ the 

 carboniferous insects are in several cases referable to 

 existing genera, as are the Arackmda, the highest group 

 of which, the scorpions, is represented in the coal by a 

 genus differing from its living congeners only in the 

 disposition of its eyes.' Now, without dwelling at 

 present upon the almost similar persistence of various 

 representatives of the different vertebrate groups, it 

 seems to me that the c persistence 3 of many of the plants 

 and of the lower invertebrate types is much more ex- 

 plicable on the assumption of successive evolutions of 

 more or less similar forms from similar starting-points 

 under the influence of like conditions, than on the as- 

 sumption that such changeable forms should have repro- 

 duced their like without any very appreciable alteration 

 through such vast and unrealizable epochs of time x ! 



1 I am glad to find that more or less similar views have also been 

 expressed by my colleague, Dr. Grant. He says : ' The existing races, 

 which alone concern us here, are not descended from each other, 

 although from more simple, common ancestry, and they do not, there- 



