THE LIVING SUBSTANCE. 55 



own internal resources, its hoarded specific environment, so 

 that for a variable time it becomes wholly independent of 

 external environment, of even the element it usually respires. 



From the formation of ectosarcal areas as external protection, 

 to the natural habit of encysting, so common among the Protozoa 

 and retained by protoplasm even among such highly differen- 

 tiated forms as rotifers, to the self-sealing habit of snails, etc., 

 and beyond these to the habits of hibernating found among 

 the higher animals, even mammalia ; the phenomena are strictly 

 to be grouped together under this interpretation. ^ 



Through a wide range of forms, protoplasm makes use of 

 ectosarcal layers for purposes of temporary isolation to a more 

 or less complete degree from the direct influence of external 

 environment. The purpose subserved may be an economy of 

 energy, and of material both as hoarded reserve and as a factor 

 of immediate environment during metamorphic changes ; or it 

 may be purely protective during adverse conditions of environ- 

 ment. A very common thing is for part of the organism, or 

 all of it with small local exemptions, to be superficially pro- 

 tected from external environment by such formations more or 

 less modified secondarily ; and such is the origin of all exo- 

 skeletons, and indeed of many endo-skeletons also. 



The lower forms, and also the higher forms in embryonic 

 stages, make large use of ectosarcal layers produced from their 

 mass so as to form distinct membranes which either produce 

 substance for a non-living membrane or themselves atrophy 

 later and are discarded after the need for seclusion is ended. 

 The striated membrane in Echinus eggs is of this sort. I 

 have watched the progressive formation of silicious capsules in 

 a fresh-water Radiolarian, Clathrulina elegans, upon a basis of 

 a coarsely vacuolate peripheral layer of ectosarc, and noted an 

 ectosarcal origin for the stalk ; I have watched also the gradual 

 formation, by progressive rearrangement of the elements with 

 subsequent chitinous transformation, of the very complex 

 capsule of the winter tgg of the fresh-water Polyzoan, Crista- 

 tella. 



These phenomena are one with the partial independence 



1 See Selection of Environment ; also Fosterhood. 



