This distinction is not drawn by physiologists, and is only implied by some by their general manner of writing. These facts, though affecting every organic being on the face of the globe, which has existed, or does exist, can only be viewed by the Creationist as ultimate and inexplicable facts. But this unity of type through the individuals of a group, and this metamorphosis of the same organ into other organs, adapted to diverse use, necessarily follows on the theory of descent{152}. For let us take case of Vertebrata, which if{153} they descended from one parent and by this theory all the Vertebrata have been altered by slow degrees, such as we see in domestic animals. We know that proportions alter, and even that occasionally numbers of vertebrae alter, that parts become soldered, that parts are lost, as tail and toes, but we know <that?> here we can see that possibly a walking organ might <?> be converted into swimming or into a gliding organ and so on to a flying organ. But such gradual changes would not alter the unity of type in their descendants, as parts lost and soldered and vertebrae. But we can see that if this carried to extreme, unity lost,--Plesiosaurus. Here we have seen the same organ is formed <?> <for> different purposes <ten words illegible>: and if, in several orders of vertebrata, we could trace origin <of> spinous processes and monstrosities &c. we should say, instead of there existing a unity of type, morphology{154}, as we do when we trace the head as being the vertebrae metamorphosed. Be it observed that Naturalists, as they use terms of affinity without attaching real meaning, here also they are obliged to use metamorphosis, without meaning that any parent of crustacean was really an animal with as many legs as crustacean has jaws. The theory of descent at once explains these wonderful facts. {152} This is, I believe, the first place in which the author uses the words "theory of descent." {153} The sentence should probably run, "Let us take the case of the vertebrata: if we assume them to be descended from one parent, then by this theory they have been altered &c." {154} That is "we should call it a morphological fact."