ON THE iNEMATODES OE THE COMMON EARTHWORM. 617 
of not being liable to contamination^ and, of affording a fairly 
clear view under the microscope of the nematodes under 
cultivation. It is open, however, to the same objection as 
the body-wall medium. Occasionally an evil odour develops, 
accompanied as-n rule by the appearance of an opaque scum, 
and all the nematodes in the culture die off. 
The dimensions to which the adult nematodes attain vary 
according to the nutritive quality of the media on which they 
are reared, their size being directly dependent on nutrition. 
Thus those fed on worm e.vtract or putrefying worm (the 
natural food) considerably outgrow those fed on peptone, 
and the latter cannot be regarded as typical of the species in 
regard to size. 
The length of life of these nematodes in a natural state will 
be considered later in connection with their life-history. In 
artificial cultm’es, the period which the larva occupies in 
reaching maturity after its removal in the nephridial stage 
from the wonn corresponds of course to that part of the 
nematode’s life which in a state of nature elapses between the 
death of its host in the soil and its appearance as an adult. 
During this period growth is exceedingly rapid. In worm 
extract maturity is usually reached in four days. But occa- 
sionall}'^ mature females have been obtained in three days and 
males in two. Decaying body-wall takes about four days, 
peptone about six. Another jjeriod, easily ascertained in cul- 
tures, is that wliich elapses between the hatching of embryos 
from the eggs of successive generations of nematodes. In 
Avorm extract this is about eight days, in peptone about ten. 
While the period of growth prior to reproduction is fairly 
uniform, the length of life of the adults kept in cultures after 
reproduction is very variable. Some females succumb to the 
effort of reproduction, others survive the process by only a 
few days, and others live on afterwards for two or three Aveeks. 
The use of an artificial culture medium shoAvs that the dis- 
tinction between oviparity and viviparity as specific characters 
does not exist in these nematodes of the earth-AAmrm. They are 
oviparous or viviparous according to the food supply. Those 
