NOTES ON THE FREE-LIVING NEMATODES. 455 



under conditions which made careful recording difficult. On 

 removing the cultures to Cambridge a new kind of peptone^ 

 was used for the preparation of a culture-medium, and the 

 behaviour of the nematodes altered considerably with this 

 change. In five generations, from the ninth to the fourteenth, 

 not a single male was produced. The interval elapsing 

 between the arrivals at maturity of successive genei'ations 

 decreased from seven days to four, and the number of fertile 

 eggs laid by each parent rose to between 150 and 300. In 

 every case the life of the individual was prolonged under 

 these more favourable (?) conditions, the period of fertile 

 production being succeeded by another at least as long, 

 during which sterile eggs were laid. 



Later, in the fifteenth generation, the peptone used in 

 Norfolk was again tried, and at once males appeared 

 sparingly in the cultures. Later the individuals raised from 

 certain batches of eggs showed a fairly high ratio (e.g. in 

 the nineteenth generation [23] 19 i 4 cJ cJ), but in general 

 males were rarer than in the early cultures of August. After 

 another removal at Christmas, 1909, the second period of 

 male production was terminated like the first. It may well 

 be supposed that the alteration of conditions, slight or other- 

 wise, which ensues on changing the place of experiment was 

 directly responsible for the disappearance of the males. 



It is not probable, however, that the proportions are 

 controlled by nutrition, for though at first circumstances 

 seemed to indicate that the use for a culture-medium of white 

 peptone acted as a stimulus to male production, from the 

 fifteenth generation onward four series of cultures were 

 maintained, two in white peptone and two in brown (which is 

 the more favourable medium for growth). As mentioned 

 above, males first appeared in the former medium, but in the 

 seventeenth generation they were also observed in brown 

 peptone, and there was no sufficient difference in the 

 figui'es to suggest which peptone was the better material for 

 the production of males. 



^ In dark brown crystals completely soluble in water. 



