96 ON CLASSIFICATION. 



Owen, in his paper " On the Characters, Principles of Division, 

 and Primary Groups of the class Mammalia," published in the 

 Journal of the Linnsean Society ; though it should be added 

 that Professor Owen made certain additions to the nucleus 

 furnished by Mr. Waterhouse, which are unquestionably 

 original. 



Thus the " Lissencephala " of Professor Owen is simply a new 

 name for the group of Mammals (" in which the cerebrum is 

 destitute of convolutions, or nearly so") indicated by Mr. 

 AVaterhouse ; and " Gyrencejihala" is a like verbal equivalent 

 for Mr. Waterhouse's group of 3 [animals characterised by 

 having the brain provided with distinct convolutions. But 

 Mr. Waterhouse does not mention Man at all, while Professor 

 Owen creates a new sub-class, Arehencephala, for the genus 

 Homo, and substitutes the name " Lyencephala " for Implacentalia, 

 formerly applied to the Omithodelpliia and Biclelpliia. 



In attempting to decide between the various classifications 

 thus presented to us, the canons by which our judgment must 

 be guided are simple enough. It is obvious, in the first place, 

 that the definition of a group, whether that definition be based 

 on cerebral or on placental characters, must be true, as a matter 

 of fact, if anv value is to be attached to the classification of 

 which that definition forms a part. 



And, in the second place, it is clear that the definition of each 

 group must be distinctive, that is to say, it must not include the 

 members of other groups. 



Applying the second canon to the classification last mentioned, 

 it appears to me to collapse at once. 



The sub-class Lissencejihala, for example, is thus defined : — 



"The corpus callosum is present, but connects cerebral hemi- 

 spheres as little advanced in bulk or outward character as in the 

 preceding sub-class ; the cerebrum leaving both the olfactory 

 lobes and cerebellum exposed, and being commonly smooth, or 

 with few and simple convolutions in a very small proportion, 

 composed of the largest members of the group. The Mammals 

 so characterised constitute the sub-class IAssencephala" — 

 L. c, p. 14. 



