ECOLOGICAL 59 



the opening of the shell a fold of skin, which secretes a lid first of 

 rapidly hardening mucus and then of lime, layer after layer of 

 carbonate and phosphate. This forms the tightly fitted winter-lid 

 or epiphragm, which is perforated by a minute hole permitting 

 interchange of gases. After the snail has finished the calcareous lid, 

 it draws itself still farther back into the shell, and makes another 

 door, quite membranous, and then another and another. There 

 arc sometimes six, all with empty spaces between them. Then the 

 creature sinks into a strange dead-alive state for nearly six months. 

 The heart beats twice or thrice a minute instead of the fifty times 

 observed in summer; the respiration is slow diffusion; the glycogen 

 or animal starch stored by the liver is used up; some of the tissues 

 seem to be in a bad way. There are many interesting points : that the 

 snail begins to make the lid at the proper time even when it is kept 

 warm, that it can be kept asleep in continuous dry cold for twenty 

 months, that if it is wakened artificially in gradually warmed water 

 it soon falls asleep again when it cools. Meisenheimer records the 

 interesting fact that snails with broken epiphragms always die 

 when subjected to a temperature of — 100 deg. C, while those with 

 intact epiphragms can survive a day or more of that terrible cold. In 

 normal cases the Roman snails become restless in April, and burst 

 their prison-doors with violence. 



Some fishes of the carp and eel tribes burrow into the mud at 

 very low temperatures (5 deg. C.) and become extremely lethargic. 

 The heart-beats may fall from 20 or 30 to one or two per minute, 

 and the weight decreases as the fat and other reserves are consumed. 

 A carp will sometimes survive being frozen within a block of ice, 

 but not, of course, if the blood freezes. In all cases rapid thawing 

 is fatal, and it may well be that the pure water produced within the 

 tissues during thawing is destructive to the protoplasm. Amphibians 

 also exhibit this winter lethargy, the frogs, for instance, betaking 

 themselves to the mud of the pond, where they lie buried, not asleep 

 in any exact sense, but with mouth shut, nostrils shut, eyes shut, 

 breathing through the skin, and with the heart beating feebly. On 

 the Continent salamanders are sometimes found wintering together 

 in large numbers. 



As to reptiles, some careful observations have been made on 

 lizards. Two or more lie together, motionless, but not rigid, with 

 closed eyes and no perceptible breathing, but sometimes with open 

 mouth. They keep the vital fire burning by consuming two fatty 

 bodies which lie near the hip girdle. It is interesting to learn on good 

 authority that our Scottish viviparous lizard sleeps for nine months 

 of the year at Archangel. A large number of slow-worms are some- 

 times found huddled together in their winter retreats. The Greek 

 tortoise normally buries itself in the ground when winter sets in, 

 and lets the current of its life run slowly. One remembers how Gilbert 



