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noticed. The characters which rank one object above another are not 

 known. Relations and analogies of the greatest importance fail to 

 attract attention, nor does he recognize a part in its many modifications. 

 Upon entering a museum sucli knowledge is again requisite to appre- 

 ciate what is gathered there. We can only pity the person who wonders 

 why bats are not with birds, or why snakes, eels and worms are in 

 different cases. 



Thi'oughout nature there are certain principles or relations which, 

 when searched for, furnish the only true guides, and very few observa- 

 tions of these show that nature has undoubtedly followed a certain 

 plan in producing organized beings. As these beings ai-e scattered all 

 over the globe, inhabiting different elements, this plan is considerably 

 altered and disfigured by modifying influences. The aim is to discover 

 this plan, to trace it through intricate paths, to recognize it in various 

 disguises, and when fully worked out, to draw the lines of demarcation 

 which serve to divide and sub-divide such groups as may be formed. 

 To accomplish this end, the affinities which one object beai's towards 

 another must be closely studied. In the animal kingdom those of real 

 importance are found in the internal vital structures, where we must 

 search for the resemblances of a permanent character. A single organ 

 or set of organs may be selected and followed through its many stages 

 but the greatest pi-ecision is obtained when the organism is considered 

 in the totality of its })arts. The extei-nal markings though not to be 

 depended upon for permanent characters ai*e found to be of value in 

 deteraiining the minor differences and forming the lesser divisions. 

 However, as the same influences that modify externally affect the 

 internal arrangement to some extent, these more crude characters 

 serve to point out the path we wish to follow. 



Such principles may be discovered in all systems having any 

 claim to be natural, their correctness depending on the closeness with 

 which the guide has been followed. In the system of Aristotle, formed 

 more than two thousand yeavs ago, we find the first evidences of a 

 natural classification. He studied closely the circulation, and separated 

 all animal life into two groups, corresponding to our vertebrates and 

 invertebrates. One he formed of all those animals possessing red blood, 

 in the other he placed all with a coloiuless fluid. His further divisions 



