Chap. I. HOMOLOGIES IN DISCONNECTED ANIMALS. 19 



general traits of relationship so characteristic of the great types of the animal and 

 vegetable kingdoms, can be understood, or even perceived. How, then, could these 

 relations have been devised without similar powers? If all these relations are almost 

 beyond the reach of the mental powers of man, and if man himself is part and 

 parcel of the wliole system, how could this system have been called into existence 

 if tliere (h)es not exist One Supreme Intelligence, as the Author of all things? 



SECTION V. 



CORRESPONDEN'CE IN THE DETAILS OF STRUCTURE IN ANIMALS OTHERWISE ENTIRELY 



DISCONNECTED. 



During the first decade of this century, naturalists began to stud}^ relations among 

 animals which had escaped almost entirely the attention of earlier observers. Though 

 Aristotle knew already that the scales of fishes correspond to the feathers of birds,' 

 it is but recently that anatomists have discovered the close correspondence which 

 exists between all the parts of all animals belonging to the same type, however dif- 

 ferent they may appear at first sight. Not only is the wing of the bird identical in 

 its structure Avith the arm of man, or the fore leg of a quadruped, it agrees quite as 

 closely with the fin of the whale, or the pectoral fin of the fish, and all these 

 together correspond in the same manner with their hind extremities. Quite as strik- 

 ing a coincidence is observed between the solid skull-box, the immovable bones 

 of the face and the lower jaw of man and the other mammalia, and the structure of 

 the bony frame of the head of birds, turtles, lizards, snakes, frogs, and fishes. But 

 this correspondence is not limited to the skeleton; every other system of organs 

 exhibits in these animals the same relations, the same identity in plan and structure, 

 whatever be the differences in the form of the parts, in their number, and even in 

 their functions. Such an agreement in the structure of animals is called their 

 homology, and is more or less close in proportion as the animals in which it is 

 traced are more or less nearly related. 



The same agreement exists between the different systems and their parts in Artic- 

 idata, in Mollusks, and in Radiata, only that their structure is built up upon respec- 

 tively different plans, though in these three types the homologies have not yet been 

 traced to the same extent as among Ycrtel)rata. There is therefore still a wide 



' Aristoteles, Hisforia Aninialiuni, Lib. I., Cliap. Sect. 4, notes 1 ami 2, and the many otiier work.*, 

 1, Sect. 4. o yun tv hovidi mtimv, tovto tr qllvt iiamphlcts, and i)ai)ers, quoted by them, wliieh are too 

 K7TI hni^. — Cimsuh also the authors referred to in ninnerous to be mentioned here. 



