Nematode found in Stomach of Cojyper-head Snake. 37 



surface (Figs. 2 and 3). The lateral field is shown both here 

 and near the middle of the body (Fig. 4), and it is seen to 

 widen as the extremity is approached. 



The nervous system consists of a ring surrounding the 

 oesophagus, and giving off several nerves to the rest of the 

 body (Fig. 5). 



The female sexual apparatus is double, only one side being 

 shown (Fig. 9). The ovary is disposed in longitudinal folds 

 and occupies 37 per cent, of the length of the body. This 

 is succeeded by a seminal receptacle, then a uterus in which 

 eggs were found in the very first stages of segmentation and 

 a vulva or sexual opening a little behind the centre of the 

 body. The eggs are spherical, as shown in Fig. ] 0. 



Finally, a formula is here given for this species, which will 

 supply some necessary particulars for the future systematic 

 placing of this worm. 



The nematode formula devised by Dr. Cobb gives in brief 

 com]3ass the various measurements which are characteristic 

 for any species, and indicates at the same time the general 

 form and size of the sexual organs. The formula read from 

 left to right, corresponds to the dimensions from head to tail ; 

 and the unit of measurement is not absolute but relative, 

 the length of the worm itself being taken as the standard, 

 and the measurements given in hundredth parts of that 

 length. Thus each number expresses a percentage of the 

 total length of the animal, adult specimens as they appear 

 in profile being always taken. The formula consists of 1 1 

 numbers, representing as many dimensions. Ten of these 

 numbers are arranged as fractions, the numerator denoting- 

 longitudinal measurements and the denominator giving 

 diameters. The eleventh number at the end is the absolute 

 length of the animal — the standard of measurement. The 

 numbers are always given in the same order, referring to 

 pharynx, nerve-ring, base of neck, vulva, and anus success- 

 ively, so that the formula is brief yet clear, and comparison 

 is easy with other species. 



The formula for the present specimen may be given at 

 first with explanatory names, and we will see how much 

 information is compressed in these eleven numbers arranged 

 in this particular way : — 



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

 Lengths .. -1 -5 3-6 67^^ 99-75 



144 mm. 



Diameters .. -2 -'6 -5 1-2 



