BY N. A. COBB. 457 



Being already familiar with the use of this formula, I am not a 

 proper judge of the difficulties that would occur to a novice in its 

 use. To me the roost obvious difficulty is that of having always 

 to consider the anus with reference to its distance from the anteiior 

 instead of, as is usual, from the posterior extremity, a difficulty 

 which should disappear with a little practice. It is much easier to 

 enumerate what seem to me the advantages of the formula. 



(1.) The position of each number indicates the dimension to 

 which it refers. The formula is thus brief, yet concise. 



(2.) The position of the nerve-ring is indicated. In properly 

 prepared specimens the position of the nerve-ring is 

 clearly to be seen, so there is no longer any reason 

 why the position of so important an organ should not be 

 entered among the characteristics. In order to see at 

 once the i-elative position occupied by the nerve-ring, 

 comparison should be made between the second and third 

 numbers above the line. It will be thus seen that in 

 the species whose formula has been given, the ring is 

 situated a little in front of the middle of the neck. 



(3.) A glance along the lower line of the formula reveals at 

 once the general form of the body. The worm whose 

 formula has been given has a somewhat cylindrical body. 

 The portion of the neck in front of the nerve-ring tapers 

 considerably. The body also tapers considerably in 

 front of the anus. This latter is patent from comparison 

 of "8 with 52"1. The vulva is central, which means that 

 the sexual organs are probably double and symmetrical. 

 Therefore the body would not be likely to diminish much 

 in size in the immediate vicinity of the vulva. Hence 

 the decrease in size (1'7 to '8) must take place consi- 

 derably behind the vulva, and therefore near the anus. 

 In very plump worms the largest of the numbers below 

 the line may rise as high as 10, in slender ones become 

 less than unity. 



