(“exis ) 
We all know that the saws of human workmen differ much 
both as to shape and size in general, and as to particular 
details (as the size and form of the individual teeth, the spaces 
between them, their wider or narrower “ set,” etc.). Carpenters 
and cabinet-makers have their rip-saws, dovetail-saws, keyhole- 
saws, etc. Special types of the same tool are employed by 
workers in metal. More than twenty “named varieties” of 
saw are listed by the dealers in surgical instruments—e. g. the 
spoon-saw (a type in which I seem to recognise certain peculi- 
arities shared by it with the Sawflies’ organs), the amputation- 
saw, ete. Every such variation in form indicates some difference 
in the circumstances of its use, ¢.g. as to the precise nature 
and situation of the incision to be formed or the character of 
the material operated on—seasoned timber, sappy living wood, 
gold, copper, ivory, bone, ete. And an expert would recognise 
at once in any such case the function especially associated with 
the peculiarities of a particular type of instrument, and could 
infer the former from the latter or vice versa. 
One would expect to find similar correspondences between 
form and function in comparing the many varied types of 
natural “saws.” The substances on which they operate differ 
physiologically in their essential structure, comprising, e.g. 
acrogenous, exogenous and endogenous organisms. Some, again, 
are comparatively dry and hard, others very moist and ad- 
hesive. The incisions produced vary in shape and situation ; 
and the precise actions required to produce them must vary 
also. Notwithstanding, I have so far quite failed to establish 
any such undoubted correlation between the special characters 
of particular “ saws,” or types of “ saw,” and the differentiae of 
the operations performed by them. I cannot but think that 
some interesting results would be obtained from an investiga- 
tion of this matter, embracing a thorough study of the 
structures and operations of all the known species, But such 
an investigation could be made only by an entomologist who 
was also an expert in botany, in physiology, and in theoretic 
and practical mechanics. 
Nor can I believe that, even so, it could be made possible to 
infer in every case the functions from the structure. It does 
not seem to be at all a universal law, that an organ is more or 
