122 MEASUREMENT. 



Unit of Measurement. 



I have adopted in this work a hundredth part of a millimetre 

 (o'oimm.), as the unit of measurement. I believe it to be the only 

 convenient measure for organisms, whose size is so variable, that their 

 maximum is often double their minimum size, and of which a con- 

 siderable number are so large that if the mikron is used, too high a 

 number (generally reaching into hundreds) has to be quoted. 



We mark this unit by three letters, c.d.m. (centiemes de millimetre). 



One c.d.m. = '0003937 English inch= io/j. (mikrons). 



End of Introduction. 



