PRINCIPLES OF NATURAL ARRANGEMENT. 339 



The Lizards are connected, again, with Birds (to which they 

 would not seem to have the slightest possible relation), by means 

 of a very curious animal not now existing, which had the general 

 structure of the Lizards ; but which had the fore-legs converted 

 into wings like those of a Bird ; and which seems to have been 

 covered with something intermediate between scales and feathers. 

 Many similar instances will present themselves in the study of 

 the Vegetable Kingdom. 



492. Hence when it is stated that a Plant or Animal belongs 

 to a particular group, it is by no means necessarily implied that it 

 possesses all the characters which are considered as marking that 

 group. Thus, to revert to an instance just now employed in 

 illustration, the structure of the feathers, which are generally 

 so characteristic of the class of Birds, is greatly modified in some 

 of the species which approach nearest to other groups ; in the 

 Emu, for example (one of the Ostrich tribe), the feathers are 

 little else than stiff branching hairs ; and in the Penguin, those 

 covering the fin-like wings resemble scales. So, again, in the 

 first Natural group of plants which we shall consider, the Ra- 

 nunculus or Crowfoot tribe, there are some species which have 

 the parts of the flower arranged in threes^ as in Endogens ; yet 

 they are not really such, for their stems are Exogenous, the 

 veining of their leaves is netted, and their embryo is dicotyledo- 

 nous. Again the common Arum maculatum (Cuckow-pint or 

 Wake-robin) has reticulated leaves ; but it is not an Exogen, 

 because its stem is Endogenous, and its embryo monocotyledonous. 

 And the Pond-weed (Potamogeton) has the parts of its flowers 

 arranged in fours ; yet it does not belong to Exogens, since its 

 leaves are parallel- veined and its embryo is monocotyledonous. 



493. In considering the value of the several characters 

 afforded by the varieties in the structure of Plants, it will be 

 convenient to follow the same order as that which has been 

 adopted in describing that structure. The Elementary Tissues 

 do not afford any means of distinction, except in regard to the 

 primary divisions, the presence of Spiral Vessels being on the 

 whole characteristic of Flowering Plants (which have been hence 

 termed Vasculares) ; and their absence being nearly constant in 



