198 PROCKEDINGS OF THE ACADEMY OF [^^pn', 



to be classified, arranged iu the genealogical system, would then be 

 that of its perfected condition, for then is to be found its furthest 

 degree of specialization. And to classify it at an earlier stage 

 would be to neglect the full degree of its evolution. This is a 

 conclusion of importance when we consider certain attempts to clas- 

 sify organisms considered wholly at embryonic and larval stages, 

 as in the so-called " embryological classifications." No objection 

 is made to consider organisms at any stage, as an ovum, an embryo, 

 a larva, or an adult, nor yet to consider a particular organ by itself 

 in any of these stages, for such examination is necessary for under- 

 standing structure and growth ; but these considerations are prelim- 

 inary to the phyletic classing of the organism, which must be done 

 Avhen it has attained its full development and is most different 

 from other organisms. Organisms at their perfected stages are 

 then the materials to be classified. 



But it is difficult to determine just what is the perfected or mature 

 stage of an organism. In general the period of reproduction may 

 be said to be the perfected stage. This would especially be the 

 case for many free-living organisms which die after reproduction, as 

 the males of most insects immediately after copulation, and the 

 females of many after oviposition. In these particular cases the 

 organisms attain their fullest development at the period of reproduc- 

 tion, and die without passing through further structural phases. 

 But in other free-living animals there are several periods of genera- 

 tion before the animal dies ; and in some animals, as in certain 

 birds, the dimensions of the body and the character of the plumage 

 change with each reproductive period — that is, the size and color 

 changes more or less with each prenuptial moult. And in mam- 

 mals, those whose reproductive period may extend over several 

 years, a gradual change of the whole organism takes place during 

 this time, so that in the stage of its last reproductive period it may 

 be quite different in its characters from what it w'as at the first. 

 Also, in species with individuals cai)able of reproduction occur some- 

 times individuals with arrested genital organs, such as the worker 

 Hymenoptera ; ft)r the latter reproductive activity cannot be consid- 

 ered the criterion of structural perfection or maturity. Then, in 

 cases of neotenia, the reproductive elements may attain their full 

 growth before the other parts of the body : the organism here is 

 reproductive! y mature before it is somatically. Again, at the stage 



