THE ANIMAL PARASITES 637 
listed in the order of their frequency. It may serve only 
as a panorama of the situation, inasmuch as determinative 
study of a group amounts to a research in itself, and the 
multiplicity of them precludes a consistent study of every 
one. The data are based upon ** cases of parasitism." 
That is, each and every worm species occurrence has been 
counted, regardless of whether it was the same species 
that has been concerned over and over again, or in dif- 
ferent anatomical positions (of different individual hosts, 
of course) or whether it was in association mth other 
parasites. 
Analysis of Table 26. 
There is a grand total of 890 cases of animal parasit- 
ism embraced in the above table, which is a suflficiently 
large number to give representative value to some phases 
of the analysis. 
In the first place nematode worms occur about three 
times as frequently as all other forms of parasites. In 
gardens where spiroptera has not figured so largely the 
proportion might be reduced to about two to one. Ces- 
todes rank a poor second, trematodes a worse third, and 
acanthocephali a very bad last. This order agrees with 
our figures of 1913(20) and with the small series of 
Nicoll.(21) The latter worker found that the order was 
not changed when pains were taken to include also such 
smaller worms as could only be obtained from the host by 
using sieves, etc. Cestodes were not likely to be over- 
looked, but very small trematodes and nematodes were 
easily passed over. 
Visceral DisxRiBUTioisr. 
As to the individual organs wliich are most commonly 
parasitized our records show that with Aves as well as 
Mammalia the intestines are the parts most commonly 
affected. The stomach ranks second for both — the pro- 
(20) Proc. Acad. Nat. Sci. Phila., March, 1913, p. 127. 
(21) Proc. Zool. 8oc. London, 1912, p. 858. 
