1902 Snails in Winter 29 



smaller animals. Be that as it may, there is no doubt that 

 large numbers of snails perish during the winter, as any 

 garden will show in the early spring, especially if the pre- 

 ceding winter has been severe. C. aspersus is particularly 

 easily found to have thus suffered. Many of these show 

 epiphragms intact, and seem to have died from stress of 

 weather. 



Every one is familiar with " thrush's stones." We notice 

 them chiefly in winter, but they are very common all the 

 year round. There is hardly any familiar wayside object 

 which so forcibly brings before us such an important series 

 of biological ideas. Only one can be mentioned here, and 

 that very shortly. It concerns the origin of the warm- 

 bloodedness of the higher animals. When we look at the 

 battening thrush and the empty broken snail-shells, the 

 advantage which the power of maintaining a high and 

 constant temperature gives the bird is obvious. But the 

 disadvantages are there too. To keep up this temperature 

 a warm-blooded animal has to do an immense amount of 

 work, both in procuring food and in transforming the 

 energy of most of this food into heat. Some of the higher 

 mammals are no doubt thankful for this necessity of taking 

 so much to eat, but when abundant food is not to hand, the 

 pains and penalties are not inconsiderable. Moreover, the 

 warm-blooded animal is certainly in the position of greater 

 danger. As a matter of fact, an increase in the complexity 

 of structure and specialisation of function, with an asso- 

 ciated greater tendency for death to ensue from slight 

 injuries, happen to coincide in our zoological series with 

 an elaborate power of heat-regulation. But apart from this, 

 the organs have to work so hard that they are no doubt 

 more liable to morbid changes which end in incapacity, and 

 they have become so tuned to a high and constant tempera- 

 ture in which to do their work that, let that temperature 

 be varied by but very few degrees, they will not only tem- 

 porarily but permanently cease to discharge that complex 

 of operations which we know as life. Subsequent results 

 compel us to believe that our sauropsidan ancestor, who 

 first discovered that he was able to so keep up his tempera- 

 ture that he could walk about in the frost and devour his 



