Ill) COMPARATIVE STUDIES ON NEMATODES— HETHERINGTON 



INTRODUCTION 



The members of the phylum Nematoda both the parasitic and free 

 living forms are exceptionally interesting in view of the varieties of struc- 

 ture existing in the cephalic region and also in view of the changes in 

 structural symmetry from the fundamental bilaterality to pseudo-radial 

 symmetry, true radial symmetry, and asymmetry. 



In the following pages the author has directed his attention to a com- 

 parative study of the symmetry and structural variety of the cephalic 

 regions existing among the nematodes, parasitic and free living, endeavor- 

 ing throughout to determine the most primitive cephalic plan from which 

 the most complicated forms were derived and the order of this derivation. 

 Furthermore, some new and valuable methods of nematode technique have 

 been devised to lessen the tedium and numerous difficulties involved in 

 preparing this material for microscopical examination either as sections or 

 toto-mounts and in addition, the question of ciliation among nematodes is 

 discussed and evidence presented for the undoubted existence of such 

 structures. 



This comparative study was undertaken at the suggestion of Dr. 

 Henry B. Ward, to whom the author at this time wishes to express his 

 sincere thanks, not only for his interest in this study, but also for permis- 

 sion to use his private literature files and material from his collection of 

 unnamed parasites. Further thanks are due to the other members of the 

 department also for their kindly help and criticism. 



SOME NEW METHODS OF NEMATODE TECHNIQUE 



The difficulties involved in the preparation of nematodes for micro- 

 scopical examination either as totos or sections can be appreciated fully 

 only by those who have made any attempts whatsoever in that direction. 

 Perhaps this fact has been one contributing in no small degree to the 

 scarcity of workers in the field as compared with other fields of zoology 

 and has at the same time been responsible in a measure for the confusion 

 of nematode literature on systematic relations through the piling up of 

 countless, meager, stereotyped descriptions, many of them based only 

 on external appearances, gross anatomical features, and measurements. 

 Few comprehensive studies exist on the gross and histological anatomy 

 or upon physiological systems of the legion of nematodes known, com- 

 parable to the works of Looss on the life history and anatomy of the hook- 

 worm or of Martini on Oxyuris curvula. 



