NOTES. 425 



dered the progress of oui' knowledge of the real effects of temperature 

 on the life of animals. 



Note 32, page 105. ' In the shallow seas of temperate latitudes, only 

 such animals can exist and preserve their reproductive powers as are 

 qualified to endure every variation of temperature which may occur in 

 tho course of the seasons — Eurythermal animals, as they may be desig- 

 nated in one word. The number of eurythermal marine animals is very 

 much smaller than the amount of species which can only live in such 

 provinces (marine) as exhibit an equable or slightly variable tempera- 

 ture — Stenothermal animals, as they have been called.' 



Xote 3.3, 2'"^^ 109- I must, however, warn the reader against the 

 assumption that every such dwarfed race was produced by the influences 

 here described. In many places, for instance, where formerly really 

 gigantic pond-muasels were found, now only quite small ones occur ; 

 and it is well known that the European oysters are gradually becoming 

 smaller. This results from the circumstance that both these mollusca 

 are capable of reproduction while they are still quite small, and now 

 never grow to their full size, because they are destroyed before they 

 have accomplished their full growth. The dwarf races of certain Libel- 

 lulEe in the south of Europe appear again to depend on other causes. 

 The multiplicity of circumstances by whose co-operation dwarf races 

 are produced appears to be very considerable ; we shall have occasion to 

 examine them somewhat more closely in another chapter. Unfor- 

 tunately no satisfactory experiments have ever been made. 



Note a, page 1\0. Winter-sleepers — i.e. animals which during the 

 winter fall into a dormant state, and remain in it for weeks, or even 

 months, without dying — are to be found in almost every group. I may 

 refer the reader to the enumeration given by Schmarda {Tkiergeogra- 

 l)hie, i. 9-11). It might be well to distinguish two groups of such 

 animals, according to whether they are warm-blooded or cold-blooded. 

 These last — as we infer from some observations merely, it is true, and 

 not from experiment — appear to possess the faculty of living a latent 

 hfe at a very low temperature, i.e. to sleep ; and if we suppose that no 

 alteration takes place in the processes of assimilation, but only a retard- 

 ation, every cold-blooded animal might fall into winter-sleep. With 

 warm-blooded animals it is otherwise. These, as is well known, are 

 easily frozen ; according to Horvath's experiments— to be more 

 exactly described presently — it is extremely probable that no warm- 

 blooded animals can become winter-sleepers but those which are able 

 to become actually cold-blooded at a suflBciently low temperature. 

 Even young animals of other species which have at birth a remark- 

 ably low temperature, almost as low as that of cold-blooded animals, 

 are incapable of enduring low temperatures for any length of time ; they 

 fall asleep, it is true, taut at the same time they die. Of course, even 

 the winter-sleepers among mammals cannot bear to be actually frozen. 



