234 Mr Potts, A Note on Vital Staining 



are visible in unstained nematodes, taken fresh from cultures where 

 they were growing under the most favourable conditions. Neutral 

 red in this case only serves to differentiate pre-existing structures 

 which are otherwise very difficult to make out. 



The function of the layer is very doubtful. It might be supposed 

 that it is digestive and the great development of the granules in 

 the anterior part of the midgut where the lumen is enlarged and 

 often contains an accumulation of bacteria and organic fragments 

 would seem to support this view. But living bacteria exist embedded 

 in or attached to the lining and appear to grow and divide freely 

 there as in a culture medium. From this observation it seems 

 possible that a symbiotic relationship exists between the bacteria 

 and the nematode which is in some way furthered by the secretion 

 of a soft lining to the gut. 



While the granular phase is often seen passing into the plastic 

 phase I have not succeeded in observing a natural evacuation of 

 this lining preparatory to the formation of fresh granules in the 

 gut-cells. I hope, however, that further study will reveal the rela- 

 tion of this phenomenon to the life of the nematode. To this end 

 it will be necessary to find out whether it is a regularly, or at least 

 frequently, repeated event. 



