214 
With our present knowledge of the Nematodes it is not pos- 
sible to draw a sharp line between the freeliving and parasitic 
forms. Thus we have the heterogene species with a parasitic and 
a freeliving generation, forms as Angiostomum nigrovenosum, com- 
mon in the lungs of frogs and Strongyloides intestinalis whose 
parasitic generation lives in the intestine of man and mammals. 
Then we have a number of species living in putrefying substances 
and plant decay, many of which are transitional forms to parasitic 
life. It is proved that several of these forms can occasionally 
become parasitic; such cases are recorded from time to time in the 
special medical literature. As to other species it is proved of late 
that they can be found both as real entoparasites in plants and 
free in the earth. That the number of these will increase con- 
siderably in future is beyond doubt. Besides these partly or facul- 
tative parasites and besides the Nematodes of putrefaction we have 
for the rest the great number of species living free in earth and 
water, which far exceed the other groups in number. As far as 
our present knowledge extends, they are not parasitic though we 
must say that the life of a great number of forms depends on 
plants or particularly roots of plants. The supposition, generally 
found in the literature that the majority of Anguillulines live in 
putrefying substances is scarcely correct. Bitschli has already 
objected to it; he writes: ,,Ich suchte diese freilebende Nematoden 
mit ganz geringen Ausnahmen vergeblich in Wasser, Schlamm oder 
Erde, die schon durch den Geruch sich als deutlich faulend er- 
wiesen. Gewédhnlich fand ich den Schlamm stark riechender Ge- 
wåsser ganz frei von unseren Thierchen, ebenso die schon angefaul- 
ten Confervenmassen auf der Oberflåche derartiger Gewåsser. Eine 
reiche Fauna unserer Thiere. entwickelt sich hingegen in reinem 
und vorzugsweise fliessendem Wasser." The species found in putre- 
fying substances are ordinarily quite distinct forms which are re- 
presentatives of a few genera, the most common of which are 
