40 SCHMIDT ON THE COMPARATIVE PHYSIOLOGY 



the possibility of his own existence being partly mediated by 

 the above most simple beings restoring the equilibrium of the 

 atmosphere. 



III. Conclusions. 



The facts which have been discussed in the preceding pages 

 may be briefly expressed as follows : — 



1. That the Articulata are characterized by the presence of a 

 peculiar substance, chitine, which constitutes the whole of their 

 external investments, as also the tracheae, the gills, and probably 

 the innermost layer of the intestinal tube ; this substance, which 

 resembles woody fibre, is not found elsewhere in either the ani- 

 mal or vegetable kingdom, and it contains exactly the elements 

 of proteine and starch or of ammonia and sugar. 



2. The substance of the cellular membrane of plants (cellu- 

 lose) is by no means peculiar to plants ; in fact it appears to be 

 very widely diffused in the lower classes of animals, and has been 

 experimentally proved to be a constituent of the mantle of the 

 Ascidice and Frustulice. 



3. The smooth and transversely striated muscular elements 

 (primitive fibres) of the Invertebrata (Cockchafer, Craw-fish and 

 Unio) are identical in composition. 



4. Phosphate of lime is in intimate relation with the process 

 of cell-formation, and probably a soluble combination of albu- 

 men with it in definite proportions alone possesses the physico- 

 chemical qualities necessary for this process. 



These facts lead to the following deductions : — 



I. No chemical or physical difference can be instituted be- 

 tween animals and plants; psychology alone must define the 

 boundary limits, if any. All those distinctions which have hi- 

 therto been made, and which have long been untenable before the 

 tribunal of sound natural philosophy are also without experimental 

 foundation, and have arisen from confusion of the relations of 

 causality : they are all mere consequences of the psychical con- 

 stitution of the individual, of the species or genus ; merely the 

 means necessary for the attainment of an object which the soul 

 of the individual or of the universe aims at. 



Proof. The most important differences in form and compo- 

 sition which have hitherto been instituted relate to — 



a. Motion. 



