OF NATURAL HISTORY. 525 



ders, genera, and fpecies, are derived. Between two clafles, 

 or two genera, however. Nature always exhibits intermediate 

 productions fo clofely allied, that it is extremely difficult to 

 afcertain to which of them they belong. The polypus, which 

 multipties by fhoots, or by fe(Stions, from its body, conne6ls 

 the animal to the vegetable kingdom. Thofe worms which 

 lodge in tubes compofed of fand, feem to link the infecSts to 

 the fhell and cruftaceous animals. Shell-animals and crufta- 

 ceous infects make alfo a near approach to each other. Both 

 of them have their mufcles and inftruments of motion attach- 

 ed to external inftead of internal bones. From reptiles, the 

 degrees of perfedlion in animal life and powers move forward 

 in a gradual but perceptible manner. The number of their 

 organs of {qxi^q, and the general conformation of their bo- 

 dies, begin to have a greater analogy to the ftru(5lure of 

 thofe animals which we are accuftomed to confider as belong- 

 ing to the more perfe£l kinds. The fnake, by its form, its 

 movements, and its mode of living, is evidently connecSled 

 with the eel and the water-ferpent. Like reptiles, moft fifli- 

 es are covered with fcales, the colours and variety of which 

 often enable us to diftinguifh one fpecies from another. The 

 forms of fifties are exceedingly various. Some are long and 

 {lender ; others are broad and contradled. Some fifhes are 

 flat, others cylindrical, triangular, fquare, circular, &c. The 

 fins of fifhes, from the medium in which they live, are anal- 

 ogous to the wings of birds. Like thofe of reptiles, the 

 heads of fifhes are immediately conne(5ted to their bodies, 

 without the intervention of necks. The flying fifhes, whofe 

 fins refemble the wings of bats, form one link which unites 

 the fifhes to the feathered tribes. Aquatic birds fucceed, by 

 a gentle gradation, the flying fifhes. 



In tracing the gradations from fifhes to quadrupeds, the 

 tranfition is almofl imperceptible. The fea-lion, the morfe, 



all the cetaceous tribes, the crocodile, the turtle, the feals, 



S s f 



