32 Traces of Unity in the 



the mudfish the single many-jointed cartilaginous style 

 may be looked upon as a fin like that of the Ichthyo- 

 saurus or common fish reduced to a single ray : and that 

 this is the right view to be taken is evident in the fact 

 that in one species of Lepidosiren a number of stylets 

 are inserted at right angles into the extremity of the 

 style for the purpose of carrying a narrow fold of fin- 

 like membrane, and that the same disposition to radia- 

 tion is exhibited still more conspicuously in the ichthyo- 

 morphous or perenni-branchiate batrachians, where the 

 single end of the digital ray of the Lepidosiren is repre- 

 sented by an appendage which is two-fold in the 

 Amphiuma, three-fold in the Proteus, and four-fold in 

 the Menopoma and Axlotes. 



Nor are these the only signs of similarity which are 

 to be met with in the limbs of vertebrate animals. On 

 the contrary, instead of being few and far between these 

 signs abound everywhere, the forearm answering to the 

 leg, the arm to the thigh, and the " scapular arch " to 

 the " pelvic arch," as the hand answers to the foot. 



The two bones of the forearm, the radius and ulna, 

 clearly correspond to the two bones of the leg, the tibia 

 and fibula : and not less clearly does the single bone of 

 the arm, the humerus, repeat the single bone of the thigh, 

 the femur. There is never any difficulty in recognizing 

 these relationships, for even in cases where, as in the 

 fish, the only parts developed ordinarily are those which 

 correspond to the hand and foot, the missing parts, or 

 at least some of them, may be present. Thus, the modi- 

 fication of the scapular fin by which the flying fish 

 can direct or retard its fall through the air when it 

 leaps out of the water, and the frog fish or angler 

 can hop briskly along the sands, is chiefly brought about 

 by the development of two long bones which obviously 



