FREE-LIVING NEMATODES 



481 



Fig. 774. Skeleton camera lucida drawing used to 

 compute the nematode formula. (After Cobb.) 

 The head end lies to the left. This gives the 

 following formula. 



1.9 8.6 14.8 46 95 

 2.8 S-2 7-4 10-4 4-3 ■ 



,81 mm. 



of bamboo splinters and differentiated into alcohol, and thence 

 successively into acid carmine in 70 per cent alcohol, 70 per cent 

 alcohol with i to 2 per cent hydrochloric acid, absolute alcohol, oil 

 of cloves and Canada balsam. The specimens thus treated are 

 more permanent than those resulting from the glycerine treatment 

 described above and are the only 

 satisfactory ones for many cyto- 

 logical studies. These various 

 treatments may affect the relative 

 proportions of the organism dif- 

 ferently, especially those of the 

 neck. It is therefore best when 

 noting measurements of specimens 

 for descriptive purposes to indicate how the specimens were treated. 

 The student cannot expect to examine the finer details of the 

 anatomy or indeed to make satisfactory progress without the patient 

 use of a good oil immersion objective under favorable conditions. 



The formula is made to convey much additional information, by 

 interspersing suggestive signs. Thus the successive signs in the ad- 

 jacent formulae indicate lips,i papillae 

 on the lips,^ a pharynx of uniform 

 'diameter without armature of any 

 kind,^ no amphids,* a renette whose 

 excretorypore is located a little behind 

 the nerve-ring,^ about 600 transverse 

 striae resolvable into rows of dots,® 

 no wings to the cuticula,^ a median 

 esophageal bulb two-thirds as wide as the middle of the neck,* a 

 cardiac bulb three-fourths as wide as the base of the neck,^ two 

 symmetrically reflexed ovaries, occupying 71 per cent of the length 

 of the body,i° no caudal glands or spinneret," a single outstretched 

 testis occupying 63 per cent of the length of the body,^^ a bursa 

 beginning in front of the anus and including the entire tail,^' 4 

 bursal ribs or supplementary organs on either side in front of the 

 anus, and 5 ribs on either side behind the anus." 





1 Conventionalized contour of the front of the head. 

 of the lips. ' Conventionalized outline "' the pharynx. 



^ Conventionalized contoui 

 ' Absence of mark indicat- 



