454 



ARABIAN NEMATODES, 



The formula which I now propose points out, by means of eleven 

 numbers, eleven dimensions, and serves at the same time to indicate 

 the sex from which the measurements were taken, as well as the 

 general form and size of the sexual organs. The following are my 

 formulae for a species of Oncholaimus : — 



Female. Male. 



1- 8-2 17-2 52- 93-3 '8 8' 16-6 M 94-1 



•9 1-5 1-6 1-7 -S^*'' -8 1-3 i-4 14 -8^'^^ 



The formula for the male is distinguished from that of the female 

 by the use of the letter M, for reasons presently to be stated. In 

 order to exhibit in as graphic manner as possible the nature of 

 this new formula, I have desired the printer to set up the above 

 formula for the female in special type as follows : — 



Pharynx. Nerve-ring. Base of Neck. Vulva. Anus. 



Lengths 1- 82 17-3 52- 93 3 



Diameters 9 1-5 16 17 .8l"77mra. 



Pharynx. Nerve-ring. Base of Neck. Vulva. Anus. 



The numbers above the horizontal line relate to longitudinal mea- 

 surements, while those below it relate to diametral measurements. 

 The first number above the line (!•) represents the distance from 

 the anterior extremity of the animal to the bottom of the pharynx 

 or buccal cavity. The first number below the line ("9) represents 

 the length of the body-diameter which passes through the base of 

 the pharynx. The second number above the line (8-2) represents 

 the distance from the anterior extremity of the animal to the 

 centre of the nerve-ring; and the number directly below (1*5) 

 represents the length of the corresponding diameter, i.e., the body- 

 diameter passing through the nerve-ring. The third pair of 

 numbers (17*3 and 1*6) represent measurements relating to the 

 posterior end of the oesophagus or base of the neck. In other 

 words, 17 '3 is the distance from the anterior extremity of the 

 animal to the posterior end of the oesophagus, or is the length of 

 the neck including the head ; and 1'6 is the diameter of the body 

 at the point where the oesophagus joins the intestine, i.e., where 

 the neck joins the body. Finally, 52 and 93'3 are the distances 

 from the anterior extremity to the vulva and anus respectively, 



