436 Mr. W. S. Savory [March 14, 



To certain structures in which this property is most plainly and 

 strongly marked the term muscle is applied ; but these structures are 

 so various in their characters, that the only common distinctive feature 

 they possess is contractility. Moreover, other forms of contractile 

 tissue occur in the animal kingdom, as certain cell- walls, or cell 

 contents or globules. Nay more, a substance, presenting no structure 

 or any definite form whatever, may yet possess this power. Now, 

 although the term muscle is not commonly applied to all these forms 

 of contractile substance, but usually restricted to those varieties which 

 assume a definite shape, and appear as fibres, yet an extended exami- 

 nation of the various forms of contractile substance which occur in 

 the animal kingdom will show that this distinction, although perhaps 

 better than any other, and sufficient for ordinary purposes, is never- 

 theless an arbitrary one, and cannot be applied in all cases. The 

 several forms of contractile substance pass so insensibly into each 

 other, that it is not practicable to point out when or where distinct 

 and isolated fibres first appear ; so that those who insist upon the 

 distinction are compelled to admit the existence of transitional forms : 

 so numerous and gradual are the changes by which special parts — 

 fully-formed muscular fibres, arise out of the general structure — 

 amorphous, contractile substance. It is at least clear that the 

 various structures, commonly called muscles, are not connected by any 

 physiological characters which distinguish them from other forms of 

 contractile tissue. We can but say of the muscles, as of all forms of 

 contractile tissue, that they are distinguished only by the possession of 

 a peculiar power. 



But a structure endowed with vital contractility is not peculiar to 

 the animal kingdom. Although much more restricted in its occur- 

 rence and extent, in the degree to which it is developed, and pro- 

 portionally in its power of action, and never, so far as we know, 

 appearing in the form of striated fibre in the vegetable kingdom ; yet 

 a tissue possessing vital contractility is found in plants. A substance 

 endowed with this power occurs in the vegetable kingdom, which, 

 in structure and function, cannot be distinguished from the simplest 

 form of animal contractile tissue. , 



The substance called ' Protoplasm ' exhibits changes of form and 

 other movements which cannot be explained by any physical property, 

 or by any extraneous influences. These movements are most remark- 

 ably shown at times in the spaces of young cellular tissue. The 

 movement termed rotation or gyration, which is often seen in the 

 contents of young " cells," and which, in some form or other, are 

 probably of general occurrence, may depend on the contractility of 

 protoplasm. They are said by those who have studied them to present 

 a close resemblance to those of Amoeba and its allies. No one has yet 

 shown a distinction of importance between protoplasm of the vegetable 

 and sarcode of the animal kingdom. 



But there are other movements in plants, the cause of which is 

 less equivocal. Such movements are not confined to the lowest 



