1859.] on the Persistent Tyjyes of Animal Life. 153 



Turning to the Mollusca, the genera Crania, Disci/ia, Lingtda, 

 have persisted from the Silurian epoch to the present day, with so 

 little change, that very competent malacologists are sometimes puzzled 

 to distinguished 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 

 Arachnida, the highest group of which, the scorpions, is represented 

 in the coal by a genus diS'ering from its living congeners only in the 

 disposition of its eyes. 



The vertebrate subkingdom furnishes many examples of the same 

 kind. The Ganoidei and Elasrnobranchii are known to have per- 

 sisted from at least the middle of the Palaeozoic epoch to our own 

 times, without exhibiting a greater amount of deviation from the typical 

 characters of these orders, than may be found within their limits at the 

 present day. 



Among the Reptilia, the highest group, that of the Crocodilia, 

 was represented at the beginning of the Mesozoic epoch, if not earlier, 

 by species identical in the essential character of their organization 

 with those now living, and presenting differences only in such points as 

 the form of the articular faces of their vertebrae, in the extent to which 

 the nasal passages are separated from the mouth by bone, and in the 

 proportions of the limbs. Even such imperfect knowledge as we possess 

 of the ancient mammalian fauna leads to the belief that certain of its 

 types, such as that of the Marsupialia, have persisted with no greater 

 change through as vast a lapse of time. 



It is difficult to comprehend the meaning of such facts as these, if 

 we suppose that each species of animal and plant, or each great type of 

 organization, was formed and placed upon the surface of the globe at 

 long intervals by a distinct act of creative power ; and it is well to 

 recollect that such an assumption is as unsupported by tradition or 

 revelation as it is opposed to the general analogy of Nature. 



If, on the other hand, we view " Persistent Types," in relation to 

 that hypothesis which supposes the species of living beings living at 

 any time to be the result of the gradual modification of pre-existing 

 species— a hypothesis which though unproven, and sadly damaged by 

 some of its supporters, is yet the only one to which physiology lends 

 any countenance — their existence would seem to show, that the amount 

 of modification which living beings have undergone during geological 

 time is but very small in relation to the whole series of changes which 

 they have suffered. In fact, palaeontology and physical geology are 

 in perfect harmony, and coincide in indicating that all we know of the 

 conditions in our world during geological time, is but the last term of 

 a vast and, so far as our present knowledge reaches, unrecorded pro- 

 gression. 



[T. H. H.] 



