214 THE ROYAL SOCIETY OF CANADA 



evolve along the same paths. If this evolution be of the nature of 

 the production of two or more kinds from one, for example ai producing 

 bi and Ci, and a2 producing b2 and C2, we have as a result that the 

 dissimilar forms bi and Ci, or b2 and C2 are more closely related than 

 are the similar forms bi and b2, or Ci and C2 Also there is the possi- 

 bility of the same form being produced in two different ways as 

 indicated above for Yb. From these considerations it seems very 

 doubtful whether our ultimate aim in classification should be a 

 phylogenetic arrangement, or not. 



The Unit in Classification 



The unit which we use in classification is the species, a thing 

 that admittedly is not capable of very exact definition. In describing 

 a species we consider those characters to be irrelevant that can be 

 shown to have resulted from unusual conditions during the develop- 

 ment of the individual, that is, we definitely exclude differences that 

 are purely environmental. In our description of a species we feel free 

 to include not only the characters of the adult, but also those of any 

 or all stages from one generation to the next. It is evident from what 

 we exclude and from what we include that we are attempting to 

 describe the heritable part of a more or less homogeneous group of 

 individuals. The only part that is heritable, that is, that is trans- 

 mitted from one generation to the next, is the germ plasm, and con- 

 sequently that it is that we are attempting to classify. We deduce 

 the nature or structure of this apparently simple, but really complex 

 thing, the germ plasm, from what it produces under certain standard 

 or natural conditions, namely from the characters of the adult and 

 of the various developmental stages leading to the adult. We are 

 forced to use these very indirect means of determining the properties 

 or nature of the germ-plasm, for we have not yet been able to determine 

 its distinctive properties directly. 



Our position in regard to organic species is similar to, but not so 

 good as, that in regard to chemical elements. We know the properties 

 of the chemical elements not only indirectly from what they produce 

 under definite conditions, namely, from their compounds, but also 

 directly from the characteristic properties of the elements themselves 

 and to such a degree that a theory of their structure is being worked 

 out. For both species and elements we deduce theoretical evolution- 

 ary series from a simple to a complex condition, without yet having 

 been able either to observe in nature or to produce experimentally a 

 single transformation in the series. 



