492 OF THE ORGANIC CELL. 



witnesses to us, if they subserve no other duty. They tell the same 

 great fact which is so loudly proclaimed by all the phenomena of the res- 

 toration of parts and renovation of tissues, that the grouping of orga- 

 nized matter into definite and special forms is not a wanton or chance ef- 

 fect, but is the direct and inevitable consequence of invariable physical 

 laws. 



Expedients are for the vacillating and weak, law is for the strong. It 

 takes from the merit of any human contrivance if the engineer has to be 

 constantly tampering with it to keep it going ; we admire the machine 

 that continues its movements without variation after it has left its 

 maker's hand. I think we can have no nobler conception of the great 

 Author of the wonderful forms around us than to regard them all, the 

 vegetable and animal, the living and lifeless, the earth, and the stars, and 

 the numberless worlds that are beyond our vision, as the offspring of 

 one primitive idea, and the consequences of one primordial law. 



CHAPTER III. 



OF THE ORGANIC CELL : ITS DEVELOPMENT, REPRODUCTION, AND DIF- 

 FERENTIATION OF STRUCTURE AND FUNCTION. 



Simple and Nucleated Cells. The Simple Cell: its Parts and Functions. The Nucleated Cell: 

 its Parts and Functions. Activity of the Nucleus. Other Forms of Cells. Cells arise by 

 Self-origination and Reproduction. Reproduction by Subdivision and Endogenously. 



The Animal Cell. Forms of Cellular Tissue. Forms of Vascular Tissue. Spiral Vessels, 

 Ducts, etc. 



Differentiation of Cells. Acquisition of new Functions. Differentiation of the Animal Cell. 



Depends on Physical Causes. Influence of Heat and Air. Epoch of Differentiation. 







THE organic cell, which is the starting-point of every organism, veg- 

 Simpieandnu- etable or animal, consists of a vesicle or shell, with included 

 cieated cells, contents. If the vesicle be of uniform thickness all over, 

 the cell is a simple one ; but if there be upon some portion of it a thick- 

 ened granular spot, the cell is said to be nucleated. 



The vesicle of the SIMPLE VEGETABLE CELL, more closely examined, 

 The simple ^ s found to be composed of different laminas or strata. The 

 vegetable cell: innermost, designated the primordial utricle, consists of an 



its wall, utri- . ' _ & /. , 



cie, and endo- azotized substance, a member 01 the protein group. On the 

 chrome. exterior of this pellicle, and, as it were, arising from its sur- 



face, lies the cell wall, which serves to give protection to the parts with- 

 in. The cell wall is not a mere extension by thickening of the primor- 

 dial utricle, as is proved by its chemical constitution ; for, though it may 

 vary in physical condition from a mere glairy mucus to a firm woody 



