408 ANNIJAL REPORT SMITHSONIAN INSTITUTION, 1955 



room, -^here it liangs motionless from some projecting shred which 

 it grasps in its jaws, while its legs, wings, and antennae are folded 

 down on the underside of the body just as they were when the insect 

 was a pupa. In many insects there is a special kind of hibernation — 

 the diapause — in which the life history is interrupted by the hiberna- 

 tion of an inmature stage. Thus some species pass the winter as 

 eggs; others do so as partly grown or fully fed larvae, or as pupae. 

 The diapause, however, is not necessarily a winter phenomenon. 

 Numerous other invertebrates likewise have their own methods of 

 hibernation; snails, for instance, creep into some sheltered cranny, 

 and shrink as far as possible into the shell after making a door of 

 hardened mucus to close its mouth. 



Many of the cold-blooded terrestrial vertebrates similarly hiber- 

 nate in some protected spot, often underground, where they remain 

 motionless with all their activities reduced to a minimum. It is well 

 known that frogs hibernate, though few people know where or how 

 they do it — in actual fact, they bury themselves in the earth, or in 

 the mud at the bottom of ponds and ditches. Toads and newts gen- 

 erally hibernate on land, tucked away in some crevice undergromid ; 

 one very rarely comes across them, and it is a matter for wonder that 

 so many millions of them can be concealed all over the coimtry every 

 winter without being more frequently discovered. Snakes and lizards, 

 too, are expert at lying up in some underground den where they are 

 safe from molestation. Adders in particular like to take up winter 

 quarters in crevices among the foundations of a dry wall, and when 

 they wake after the winter they may often be seen basking in the early 

 spring sunshine on some favorite warm stone before the growing 

 herbage shoots high enough to conceal them from view. 



Even some of the marine fish cease their usual activity in the winter, 

 become torpid, and undertake a sort of hibernation. They are mostly 

 those species that live upon the plankton, the mass of floating "water 

 fleas" and other small animals and plants that swarm in such incredible 

 quantities in the upper strata of the sea during much of the year. The 

 basic organisms of the planktons are the diatoms, minute unicellular 

 plants that start multiplying in countless millions with the lengthen- 

 ing hours of sunshine in the spring. Just as all flesh is grass, so all fish 

 is diatom, for when this outburst of plant growth comes in the spring 

 the herds of copepods and other minute floating Crustacea increase 

 enormously and graze down the rich feeding that is provided for them. 

 Some of the larger fishes — and the whalebone whales, too — are special- 

 ized for feeding upon this great abundance of animal life when it 

 becomes available to them, and they filter out the swarming plankton 

 as they swim through the sea water; among the fishes the mackerel 

 and the basking shark may be particularly mentioned here. But 



