are indicated by the terms, first, second, third, etc., the 

 cephalic member of the series is the first. 



Example. — The Jirst abdominal segment is the one nearest the head. 



When the series forms a part or the whole of an append- 

 age of the body, the first member of that series is the proxi- 

 mal one. 



Example. — The Jirsi segment of a leg is the one which is articulated to 

 the body. 



The direction of an appendage does nof modify the above 

 rule. 



Example. — The Jirsi segment of an antenna is the one which is articu- 

 lated with the head ; notwithstanding that when the antennae are directed 

 cephalad, as is usually the case, this segment is the one nearest the caudal 

 end of the body. 



Intermediate. — In order to avoid ambiguity the word 

 mesal and its derivatives are used only with reference to the 

 meson. The second member of a series of three similar parts 

 is designated as the intermediate one. 



Limitations to accuracy. — As the body of an animal 

 presents but few plane surfaces or straight lines it is often 

 impossible to describe the position or direction of a part with 

 absolute accuracyc Practically, however, one will meet with 

 but few serious difficulties. Thus in describing the direction 

 of a curved or undulating line on the surface of the body it 

 will rarely be necessary to do more than to give the general 

 direction of that line ; the reader will understand that it fol- 

 lows the sinuosities of the surface of the body. 



