444 F. A. POTTS. 



and grow rapidly. Tlio rate of increase is very great : a 

 single individual wlicii once it lias become mature will in 

 five or six days give rise to one or two liundred, the eldest ot 

 wliicli will 1)0 beginning to lay eggs. But a short interval 

 then elapses bi-tween the migration of encysted larvaj toward 

 the putrid meat and the appearance of the swarms of young 

 worms of the second generation. 



It is j)erfectly easy to keep free-living nematodes in drops 

 of a nutrient iluid^ and observe under the microscope every 

 stage of their growth and i-eproduction. Each of these drop- 

 cultui'es is contained in a solid \Yatch-glass and secured against 

 evaporation byavaselined glass cover. Solutions of peptone 

 were adopted as convenient culture media, and used almost 

 exclusively in these experiments. 'J'he solutions were first 

 allowed to putrefy till a cloudy growth of bacteria had 

 developed tliroughout the liquid. So favouraljle an environ- 

 ment for growth does a peptone solution in this condition 

 constitute, that in four days the eggs laid by a mature 

 hermaphrodite nematode have themselves produced mature 

 individuals. It is only in the presence of great numbers of 

 bacteria, or the substances formed by them, that the nema- 

 todes thrive so well. In stei-ile solutions growth is suspended, 

 and eggs are only laid at long intervals, for apparently 

 nematodes find it difficult or impossible to assimilate peptones 

 in an unaltered condition. It has not been discovered whether 

 digestion takes })lace by the secretion of juices dissolving 

 the protoplasm of the Itacteria, or is merely confined to the 

 absorption of soluble substances present in the culture fluid 

 and prepared by the action of bacteria. If the second 

 alternative be correct, then a parallel is established with the 

 parasitic nematodes which nourish themselves on the dissolved 

 and broken-down food of their host. An easily observable 

 phenomenon of nematodes in culture is the rapid pumping 

 action of the second oesophageal bulb and the rectum, and 

 it may be argued from this that the nutriment obtained from 

 the stream of fluid so constantly passing through the alimen- 

 tary canal is in the form of easily abstracted soluble substances. 



