CHAP. II. ON EXTINCT ANIMALS. 41 



reason is there to suppose any one has heen abstracted 

 from the living races ? To this we would simply re- 

 ply^ that such a conclusion is home out by every prin- 

 ciple of analogical reasoning. Throughout the whole 

 of the vertebrated classes^ it is solely in groups where 

 congenial forms have been found in a fossil state that 

 we find the gradations in the living series broken and 

 interrupted. Very few such interruptions^ for instance, 

 occur in the class of birds, and they are so slight as 

 hardly to merit such a term : this fact, in our esti- 

 mation, at once accounts for the extreme rarity of the 

 remains of birds in a fossil state; scarcely any having 

 been exterminated. The living series is, consequently, 

 almost perfect. Not so, however, among the reptiles. 

 In that class there is an entire order (the Elaniosaures) 

 which has been so absolutely exterminated that .not a 

 living example remains ; hence, but for the fossil bones 

 of the Ichthyosaurus, Plesiosaurus, &c., there would not 

 merely be a wide and violent disruption of the reptile 

 series, but an absolute impossibility of forming even a 

 rational conjecture as to its course ; at least, in that 

 dissevered portion which these extinct reptiles actually 

 fill up. But we will bring this theory more home to 

 our present purpose. There is no circular series of living 

 Testacea, wherein is found every modification of form 

 necessary for unquestionable connection, more perfect 

 than that of the predaceous shell-fish {^Gasteropoda 

 Zoophaga): hence the extinct fossil species are not only 

 rare, but they nearly all belong to genera now living, and 

 therefore termed recent. Any one family in this group, 

 in short, contains more species and genera than are now 

 known in. the entire tribe of Nudihranchia, or in the 

 family of Branchiopoda. What, then, are the legitimate 

 deductions from these facts ? We must take our choice 

 of these two : — Either we are to suppose that Nature at 

 first made these latter groups as imperfect as they now 

 are, while all others, abundant in recent species and 

 forms, are perfect ; or that she has removed from the 

 creation most of those links which would fill up the 



