( XXX ) 



up. It is hasty to generalise from a limited group of auimals, though biologists 

 are nowadays in the habit of doing so. Every group first recjuires independent 

 investigation before a rule found to be true in another group can bo pironounced 

 to be true also in the one under consideration. The " laws " of development 

 have all a premiss : they are true only under certain conditions. The scientist 

 must, therefore, always remain aware that the unexpected may happen, and 

 individual cases turn out to be exceptions. For instance, what the classifier 

 considered to be a generalised character may turn out to be a specialisation, and 

 what is a specific difiereuce in one group may only be seasonal in another. 

 Since the classifier is iu the same position as the commentator of a boolc which 

 is written iu a language only imperfectly known to him, and from which many 

 words and whole pages are missing, there is necessarily a certain amount of 

 assumption in classiticatory work which makes the results projiortionately unstable. 

 However, the degree of instability can be lessened to a great extent. Just as we 

 know a jiviori that a certain character which appears generation after generation 

 in the larger number of individuals of a species will finally be present in all 

 (if the conditions of life remain the same), so the probability of the correctness 

 of a conclusion in classification will become certainty, if all the details of the 

 animals and all the facts of their biology render it probable that the Conclusion 

 is correct. 



In order to api)roach this certainty the classifier has to give his conclusions 

 the widest possible basis. The results of anatomy and morphology must be 

 checked oft' by biology, and the cDUc.lus'ons derived from one organ by the 

 conclusions based on every other part of the body. If one organ contradicts 

 the other, there is a mistake either in observation or in interpretation. The 

 more snch mistakes are discovered and corrected, the safer the superstructure of 

 conclusions will be. Grouping the animals according to the apjiarent develop- 

 ment of one organ leads to an artificial arrangement ; grouping them in 

 accordance with all organs checked oS" by biology results iu a final classification. 

 However, finality, even if the classification is restricted to a small group of 

 beings, entails such an enormous expenditure of energy that it can be approached 

 only gradually in the course of time by continued co-operation between the 

 various lines of research. 



All classification begins with the discrimination between individuals. Every- 

 body distinguishes between the specimens he observes around him and brings 

 them into groups, thus setting up a rough kind of chissiKcation. Experience 

 shows which individuals stand in the po^-sibly closest blood-relationship— that of 

 parent and olfspring, and of brothers and sisters. The classifier starting with 

 this experience, which can be corroborated over and over again, has therefore as 

 foundation for classification a solid fact which will remain firm when a flimsy 

 superstructure that a wild fancy may think fit to erect is blown away. Obser- 

 vation of the individuals so closely connected as parents and offspring teaches us 

 that there is always a certain amount of corporeal difference between them, every 

 individual having an individuality. We notice this variability iu all organs 



