226 Tb A NS ACTIONS OF THE AMERICAN INSTITUTE. 



oviparous and edentulous, liaving always two legs and two wings, 

 clothed with feathers, and liaving tlie jaws protected by a horny sheath, 

 and yet in some species the wing is rudimentary and actually rtsem- 

 bles the fin or flipper of a turtle, and is used by certain birds in 

 swimming. 



The narrow limits of a single lecture will not allow us to dwell on 

 the many singular modifications of the hind limbs of birds, nor can 

 we spend the time we would like on the locomotive appendages of 

 the mammalia, though we must allude to the Avhale as a low mam- 

 mal, in which the hind legs are rudimentary or wanting, and th» 

 fore legs are changed to fins or flippers. The tail having broad, 

 lateral fins, and the animal moving that portion of the body in a 

 vertical direction, and not from side to side as in the fish. 



At the commencement of the lecture we referred to another prin- 

 ciple of classification we were to illustrate, and this is the principle of 

 cephalization, first enunciated by an American naturalist, Prof. J. 

 D. Dana of Yale college. As Prof. Dana says, the importance of a 

 head to an animal all understand, and it makes all the difit'ereneo 

 between the typical animal, and the typical plant. An animal may 

 be called a fore-and-aft structure, while the plant is an up-and-down 

 structure. The animal has more or less will emanating from the 

 head producing voluntary motion, and an animal is typically a for- 

 ward-moving or a go-head being, while a plant simply stands and 

 grows. An animal however simple, knows enough to steer clear of 

 obstacles, i» its movements, or attempts to, at least, while a plant is 

 utterly a non-percipient, unknowing thing. 



As the head is the seat of pqwer in an animal, it is natural, that, as 

 the body more or less contributes by its members to the purposes of 

 Itiie head, so we should have relative grade or standing clearly indi- 

 cated. " Cephalization is then simply the degrees of head dominion 

 in:t'iie structure." 



.'It lis evident that animals which are fixed or attached through life 

 to one spot, represent a vegetative condition, and also that in those 

 animals in which the head is not clearly manifested, as in the jelly 

 fishes and star fishes, where the mouth is ap])arently in the center of 

 the body, and the parts surround the mouth equally, that here we 

 have a low phase of life. Among the shell fish, or mollusca, we have 

 . ahead apparent for the first time. Let us now examine this branch, 

 .andv\v€.shpJl find tliat among the lowest members the head is barely 

 Undicatfci:!,, while in tthe highest members the head is strongly specialized. 



