144 Causes and Course of Organic Evolution 



and cell-divisions all continue their course; while changes 

 preliminary to, if not actually culminating in, formation of 

 asexual cells go on, as in spore-formation of Pilobolus and 

 Miicor. Now, on account of the food-transformations and 

 conveyances that we know to proceed then, as well as from 

 the manner in wliich, succeeding to this rest period, plants soon 

 after attain to their maximum of diurnal activity, animals to 

 their most active and excitable phase, it seems almost assured 

 that such sleep movements represent stated periods, when the 

 centers of most active cognitic energy-expenditure become 

 dormant and passive, when by transformation of supplies of 

 chemic, possibly electric, and specially of biotic, energy, there 

 is gradually elaborated a potential or intra-molecular store of 

 future kinetic cognitic energy, which, on reaching a definite 

 post-nocturnal optimum, causes "waking" of the plant or 

 animal, accompanied by a sense of renewed activity and alert- 

 ness for reception of, correlation of, and response to environal 

 stimuh. 



A closely similar condition is that already treated of in the 

 annual or perennial dormancy of plant-parts and of many 

 animals. The carefully prepared for winter dormancy of 

 temperate and sub-arctic plants, and almost as strikingly of 

 many xerophytic or sub-xerophytic tropical plants, represents 

 a steady reduction of the cognitic capacity for response, and 

 a sluggish continuance mainly of the biotic. 



The wavering periods of dormancy, however, that at times 

 alternate with growth and sensitive response during mild 

 \^-inters, prove that the entire event is not that of a "not living" 

 state, but of dormancy that varies according to the specific 

 organism studied, or the degree of environal "rigor" to which 

 the organism is exposed. 



So also the frequent hibernations of animals, specially of 

 fresh water or land types, like the rotifers, snails, spiders, 

 many insects, a few fishes, many amphibians, reptiles, and 

 mammals, all represent an adaptation of the chromatin sub- 

 stance to the varying environal changes that the animal has 

 to pass through. Here however, unlike sleep, since the period 



