and its Significance in Systematic Zoology. 83 



Every one knows, whether he have thought about it or other- 

 wise, that the four Vertebrate classes are homomorphically con- 

 nected. Thus there are Flying Mammals, such as the Bats 

 and Flying Squirrels (Pteromys), uniting them with the Class 

 Aves i as well as that anomalous Monotreme, the Ornithorhyn- 

 chus, or Web-footed Duck-bill. The Edentata among Quadru- 

 peds connect them with Reptiles, by means of the Armadillos, — 

 the Great Armadillo {Dasypus gigas), and preeminently the 

 Mataco (D. Apar), being homomorphic of the Testudinata, while 

 to the Saurian Reptiles they are united by the Scaly Pangolins 

 (Manis), and to tne extinct Pterosaurians (Pterodactyles), again, 

 they are united by the Bats. With Fishes, the Mammalia are 

 most singularly connected by the Cetacea ; while a special re- 

 semblance appears between the Narwhal (Monodon) and the 

 Swordfish (Xiphias). 



The homomorphic resemblances between Birds and Reptiles 

 are not striking ; but the Draconine Saurians or Flying Lizards 

 (Draconis, sp.) supply examples, and the extinct Pterodactyl 

 once afforded another ; while with Fishes the various species of 

 Flying-fish (Exoccetus) among the soft-finned, and Flying Gur- 

 nards (Dactylopterus and Pterois) among the hard-finned, are 

 good illustrations. It only remains to connect Reptilian forms 

 with Fishes; and here the Snakes (Ophidia) may well be com- 

 pared with the Eels ; and less striking instances of resemblance 

 occur between the Saurian reptiles, such as the Alligator, and 

 the bony-cased Sturgeon, and between the Testudinata and the 

 Trunk Fishes (Ostracion). Perhaps also that great Enaliosaur 

 the Ichthyosaurus might be here mentioned. 



Without extending my illustrations too far, I will select the 

 Mammalia as an example of the recurrence of form within the 

 limits of a single Class. The organic structure and affinities 

 of one Order are dissimilar from those of another, just as the 

 structure and affinities of one Class differ from those of another ; 

 the difference between Class and Order being one of degree, and 

 not of kind ; so that it is as remarkable to find resemblances of 

 form in widely separated Orders as in still more widely sepa- 

 rated Classes, although, of course, homomorphic resemblances 

 are more striking between Orders than between Classes. In the 

 Order Quadrumana, for instance, we shall find representative forms 

 of various other Orders. Thus the genera Midas and Iacchus, 

 known as Marmozets, true Platyrrhine Quadrumana, represent 

 the Rodentia through the genus Sciurus (Squirrel) ; and the 

 Douroueouli (Nyctipithecus felinus), in the same division, repre- 

 sents the Cat {Felts) in the Digitigrade Carnivora ; while, among 

 the Strepsirrhine Quadrumana, the Loris (Stenops tardigradus) 

 represents the true Sloths in the Order Bruta, and the very 



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