142 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



prolific than the carnivora, as they must be to keep up the supply of 

 food. Insectivorous birds are very abundant, but they are not numerous 

 enough to keep the plant-eating molluscs and insects in check, and the 

 devastation which is caused every year by the armies of grasshoppers 

 and locusts and herbivorous beetles and by other less conspicuous insects, 

 shows that their natural enemies are not numerous enough to overtax 

 their productive power. 



The birds which feed upon grain and seeds and fruit are very 

 abundant indeed, and they sometimes gather at their breeding grounds, 

 or places of assembly, in innumerable multitudes, but the hawks and 

 owls which prey upon them are never numerous. 



The small rodents, such as the rats, mice, squirrels and rabbits, are 

 the most abundant and prolific of animals ; but the small carnivora are 

 so rare that their very existence is known to few except naturalists and 

 trappers. 



The homes of the wild sheep and goats, deer, antelopes, cattle and 

 horses support these large mammalia in incredible numbers, but their 

 carnivorous enemies are never abundant. It is clear that if the destruc- 

 tion of the plant-eaters exceeded their productive power, both herbivora 

 and carnivora would disappear, and terrestrial life would come to an end. 



The animal life of the ocean shows a most remarkable difference, for 

 marine animals are almost exclusively carnivorous. 



The birds which live upon the ocean, the terns, gulls, petrels, divers, 

 cormorants, tropic birds and albatrosses, are very numerous indeed ; so 

 numerous that in many parts of the ocean some are always visible in 

 calm weather around the vessel, wherever it may be. The only parallel 

 to the pigeon-roosts and rookeries of the land is found in the dense clouds 

 of sea-birds around their breeding places, but these sea-birds are all car- 

 nivorous; most of them are fishers, and others, such as the petrels, 

 scoop up the copepods and pteropods from the surface. Even the birds 

 of the sea-shore subsist almost exclusively upon animals such as mol- 

 luscs, Crustacea and annelids. 



The seals pursue and destroy fishes ; the sea-elephants and walruses 

 live upon lamellibranchs ; the whales, dolphins and porpoises, and the 

 marine reptiles, all feed upon animals, and most of them are fierce 

 beasts of prey. The manatee is a vegetable feeder, but it is not strictly a 

 marine animal, since its home is in the mouths of great rivers. 



There are a few fishes which pasture in the fringe of seaweed which 

 grows in the littoral zone of the ocean, and there are some which browse 



