ECOLOGICAL 63 



the old popular notion of all these varied phenomena in terms of 

 sleep — say, rather, as evolving from some of its deeper phases, and 

 with their longer periods of seasonal operation to dwell in? Or at 

 least, have not these seasonal phenomena, and the ordinary nightly 

 one (or ones) of sleep, some traceable development from that 

 relatively passive state which follows the cessation of ordinary 

 daily activities as far as may be, consistent with the mainten- 

 ance of the more or less slowed-down machinery of life {see 

 physiological section on Sleep). 



It is difficult to discover the most natural arrangement for the 

 various phases of reduced vitality which we have illustrated; and 

 in any case they must not be thought of in linear order, since they 

 are analogous adaptations to difficult conditions, and have probably 

 arisen many times independently in different phyla. 



Perhaps it would be clearer to separate off the cases of dormant 

 eggs (and even seeds) since these are reproductive adaptations and 

 not adult individual ones. 



It may also be clearer to separate off the encystment of Protozoa, 

 since this must be thought of in connection with their unique power 

 of evading natural death. Yet it is certain that in some adult multi- 

 cellular organisms there are processes of rejuvenescence during the 

 long rest of a dormant or encysted phase. 



The difficulty of natural arrangement is further illustrated by 

 cases like chrysalids, where the quiescent pupa undergoes an histolytic 

 de-differentiation (in varied degrees of intensity) and is built up on 

 the new architectural plan of the adult insect. The pupation may have 

 been a seasonal adaptation to begin with, but in many insects it 

 may be evaded for several winters, while, on the other hand, there 

 may be successive pupations in two or more summer generations. 

 When the histolysis or tissue-dissolving of the larval organs and 

 tissues is very thoroughgoing, as in most Dipterous Flies, there must 

 be very intense metabolism in the "imaginal folds" or discs of 

 rejuvenescent cells which form the foci of the resumed development. 

 The following scheme is suggested: 



I. Arrest of Vital Processes, sinking down to lethargy, yet without 

 adaptive structural change, as in dried-up Nematodes, 

 Rotifers, and Crustaceans. 

 II. Encystment, when there is a protective investment, as in the 

 winter snails, many Protozoa, seeds, etc. 



III. Lethargic Torpor, when the everyday functions approach a 



standstill, as in frogs and reptiles in their winter retreats. 



IV. Comatose condition in those mammals, such as badger and 



bear, which do not hibernate (in the strict physiological 

 sense), but are often very sleepy and may doze for days. 

 This is nearest normal sleep. 



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