ON THE NEMATODES OP THE COMMON EAETHWOEM. 613 
merely by transferring a mature female of one generation 
into a fresh watch-glass, in which it may become the pai’ent 
of a further generation. 
The temperature at which the cultures were carried on was 
the ordinary temperature of the laboratory. 
For the liquid in the watch-glasses into which the nematodes 
were put ordinary tap-water or salt solution was used. It 
Avas first filtei’ed to remove any nematodes Avhich might be 
present in it. The culture medium was then added, and 
replenished afterwards from time to time as required. 
If, as often happened, the medium in the watch-glass 
became too cloudy to alloAv direct examination of the 
nematodes under the microscope, they had to be removed 
singly on the point of a needle or a few at a time by means 
of a fine pipette, and transferred to a drop of Avater on a 
slide. Nematodes lying in Avater or in the nutritive medium 
in a Avatch-glass can be examined under the microscope Avith 
a low, but not Avith a high poAver. For examination with the 
high poAver they must be transferred to a slide. 
Various media have been employed. They are here given, 
roughly in the order in which they Avere tried. Most of them 
Avere abandoned as useless, and none have proved altogether 
satisfactory. The nematodes inhabiting' the Avorm Avere 
found exceedingly difficult to rear. From some cause not yet 
understood, Avhole cultures have died off quite suddenly and 
unexpectedly, breaking the continuity of experiments and 
rendering it in many cases impossible to obtain conclusive 
results. The explanation for this may perhaps lie in the 
peculiar conditions in Avhich these nematodes live. But, in 
addition to the sudden and unaccountable deaths of Avhole 
broods of nematodes in cultures Avhich began promisingly, 
great difficulty was frequently experienced in the starting of 
cultures. Again and again every one of the larvae removed 
from the nephridium died as soon as introduced into the food- 
medium. The difficulty of maintaining the cultures in a 
healthy state was on the Avhole not so great as that of making 
a successful start. 
