No. 3.] STUDIES ON CEPHALOPODS. 257 



plasm is identical, because no difference is recognizable by any 

 means at our disposal, would be an error. Deep within the two 

 particles of protoplasm which give rise to two different organ- 

 isms, there must be a corresponding difference which lies at the 

 bottom of all differences. In short, the eggs of two different 

 animals must be supposed to differ in their elementary consti- 

 tution, as much as their adult organisms differ in anatomical 

 structure. " From general scientific principles," says Professor 

 Sachs,^ "we must assume that for each visible external dijference 

 of organ ^ there is a con'esponding difference in its material sub- 

 stance, exactly as we regard the form of a crystal as an expres- 

 sion of the material properties of the crystallizing substance." 

 And again, says the distinguished German botanist, " Even the 

 different shapes of the two sexual cells — of an antherozoid or a 

 pollen grain compared with the oosphere — indicate plainly that 

 both are constituted differently as to material, since the external 

 form as well as the internal structure of any body is the neces- 

 sary expression of its material constitution. Difference of form 

 always indicates difference of material substance." This doc- 

 trine of Form ajid Matter, or of MecJianism and Function as 

 expressed in the language of physiology, is the basis of our bio- 

 logical inquiries. As is clearly expressed in the words of Pro- 

 fessor Burdon Sanderson,^ we must assume " tJiat every appreci- 

 able difference of strnctnre corresponds to a difference of function ; 

 and conversely, each endowment of a living organ must be 

 explained, if explained at all, as springing from its structure" ; 

 or, in short, we must hold to the principle " that living material 

 acts by virttie of its structure, provided we allow the term struc- 

 ture to be used in a sense which carries it beyond the limits of 

 anatomical investigation, i.e. beyond the knowledge which can 

 be attained either by the scalpel or the microscope." Given 

 protoplasm of definite structure, and we have its definite func- 

 tion or property. Or conversely, we observe a certain property 

 in a given mass of protoplasm, and we regard it as springing 

 from a definite structure. When structure varies, the function 

 must vary also ; and when we observe certain peculiar proper- 

 ties we must ascribe them to peculiarities in structure. 



1 Sachs: Lectures on the Physiology of Plants. 1887. 



2 Burdon Sanderson: Presidential Address to the Section of Biology, British Asso- 

 ciation for the Advanceme7it of Science, 1889. Nature, Vol. 40, No. 2Z 



