38 Proceedings of the Royal Society of Victoria. 



In the first fraction, referring to the pharynx, the numerator. 

 (■]) denotes the distance from the anterior extremity to the 

 base of the pharynx, or buccal cavity, and the denominator 

 (■2) represents the diameter of the body at the base of the 

 pharynx. 



In the second fraction, relating to the nerve-ring, the 

 numerator (5) denotes the distance from the anterior 

 extremity to the centre of the nerve-ring, while the 

 denominator (-3) indicates the body diameter passing through 

 the nerve-ring. 



In the third fraction, referring to base of neck, the 

 numerator (3"6) denotes the distance from the anterior 

 extremity to the posterior end of the oesophagus, or base of 

 the neck; or in other words, is the length of the head and 

 neck combined. The denominator ('o) represents the 

 diameter of the body at the point of junction of the 

 oesophagus and intestine, or where the neck joins the body. 



In the fourth fraction, relating to the vulva, the numerator 

 (67) denotes its distance from the anterior extremity, and 

 the denominator (1-2) the diameter of the body there. A 

 further reference is introduced here, placed above and to the 

 right of the numerator, to indicate the percentage of the 

 body occupied by the sexual organs. The number 37 

 indicates that they occupy 37 per cent, of the entire length 

 of the body, or more than one-third. 



In the fifth and last fraction, relating to the anus, the 

 numerator (99 "75) denotes its distance from the anterior 

 extremity, and the denominator (4) the diameter of the body 

 there. 



It must be clearly understood that relative dimensions and 

 not absolute measurements are given, for relative and not 

 absolute sizes are of prime importance for systematic purposes. 

 However, if the actual measurements are desired, they may 

 easily be calculated by dividing the body length, 1-i-l mm. 

 by 100, which gives the unit of length for the various parts. 

 This unit is ]"44 mm., and the absolute lengths will be as 

 follows : — 



Body leugth . . . . 14:1 mm. 



Length of head .. .. .. ., -144 mm. 



Length of neck . . . . . . . . 5-040 ,, 



Length from base of neck to vulva . . 91-2U6 ,, 



Length from vulva to anus .. .. 47'lt'>0 ,, 



Length of tail -360 „ 



144- mm. 



