THE long-drawn-out discussion on biological terminology which has been a feature of the past year's numbers of NATURE has certainly supplied some food for thought. The state of Denmark may not be so rotten as Sir Archdall Reid believes, but no one who shares his enthusiasm for lucidity will maintain that biological terms are as crisp and unambiguous as could be wished. The reasons for vagueness are not far to seek. The first applies to all the sciences: that concepts change their content from age to age while the words remain the same. This applies to chemistry and physics, and even to mathematics; it must a fortiori apply to a young science like biology. Fresh facts demand that some alteration be made in the frames in which they have to be included-terms like ‘organism,’ ‘development’ ‘variation’ ‘heredity.’ The terms must remain, but their content requires continual readjustment. Sometimes, no doubt, new terms are needed, but the invention of good terms is a rare gift.