KEY TO THE PHYLA AND THE MORE COMMON 



CLASSES AND ORDERS OF ANIMALS, CHIEFLY 



AQUATIC, IN THE REGION OP 



URBANA, ILLINOIS 



Directions For Using Key. The use of the following key 

 involves a series of choices between two contrasting possibilities, 

 thereby making necessary a complete chain of observations and 

 conclusions. If any one of these is incorrect, there is no possibil- 

 ity of making a correct final determination so the work must be 

 started from the beginning again. For this reason care should 

 be taken at each step to avoid "getting off the track." Always 

 make direct observations upon the animal rather than rely on 

 memor}' or on what some one else tells you. 



In using the key the two numbers at the left refer to the two 

 contrasting possibilities. Thus an attempt to classify an earth- 

 worm will start at 1 by reading the description there to see if it 

 agrees with the facts of structure in the earthworm. The state- 

 ment under 1 agrees with the facts discovered by examination 

 of the specimen so the 3 at the end of the line indicates the next 

 step to be tried. Since the earthworm is bilaterally symmetrical, 

 step 3 must be disregarded and its alternative 6 used. Then 

 comes the choice between 7 and 15, and so on until the name 

 of the phylum is reached. After the name of the phylum, is 

 given a page number which refers to a key for distinguishing the 

 smaller subdivisions of the phylum. In most cases classes and 

 orders are given. The limit beyond which this key must not be 

 used is indicated by the lack of the reference number at the end 

 of a line following the name of a class or an order. 



Laboratory notes on the work in classification are to be kept 

 in the following manner : Make a record of the steps taken (dis- 

 regarding the alternatives which have been discarded as not 

 applicable to the specimen in question). Use a line for each 

 number accepted and after the number indicate by a brief 



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