272 Proceedings of Indiana Academy of Science 
swallowed and excreted from the body with the faeces. The embryos 
then moult and withdraw within their skins, which form a sort of cyst, 
protecting the larvae from extremes of heat or cold and dryness until 
conditions are suitable to their growth. Under favorable conditions 
the second generation of worms appears in from four to six weeks and 
further generations continue to appear at this interval for about four 
months. This period of increase is generally followed by a standstill 
of about three months when the increase again starts. The thick, slow 
moving embryos die almost immediately when placed outside the body.” 
In addition to repeating the above experiments two other alterna- 
tives were tried, namely, to determine the possibility of some inter- 
mediate host, and to see to what extent these parasites develop within 
the soil. 
THEORY OF FREE-LIVING GENERATIONS. 
The common occurrence and wide distribution of these worms sug- 
gests a comparatively simple life history. Before proceeding further, 
it might be well to emphasize the fact that much confusion still exists 
between these species of lung-worms. This difficulty is, however, more 
nominal than real, because even with the unaided eye both species of the 
males at least, can be readily distinguished. By plunging a mass of 
these worms into a 30 per cent solution of alcohol in a watch glass, 
and inspecting them against a black background, there is little diffi- 
culty in separating the two species. The males of M. apri are more 
transparent, more tightly coiled and slender, than is the case with M. 
brevivaginatus. The females of the former species are also more 
slender and average about 4 cm. in length. The following averages 
(obtained by measuring one hundred males of each species) give first 
the body length, and second, the length of spicules. 
M. apri. M. brevivaginatus 
length OL POGY i... ww ws a Pat, CMR ae” 14.16 mm. 18.50 mm. 
Lengths OL, Bpiculess +... krs 20.5 ¥ o 3v)es wal « 3.80 mm. 1.25 mm. 
An examination of twenty lesions from as many different hogs, 
showed the presence of both species of lung-worms in thirteen cases. 
Of the remaining seven lesions, five contained M. apri, and three con- 
tained only M. brevivaginatus. These results would indicate that this 
last species is much more common than is generally supposed. Ex- 
perimental evidence seems to indicate that most females over 4 ecm. 
in length, and the larger eggs (mentioned under description) belong to 
this species. 
Attempts to duplicate the work of Dr. von Linden were in the 
main unsuccessful. Most of the points she mentioned were repeated, 
but the conclusions did not always coincide. The following tabulation 
gives the results obtained, together with their probable interpretation. 
Structural differences were invariably found due to sex, especially 
if the larvae were well advanced in their development. This differentia- 
tion began to appear in the second week of growth when the larvae 
were grown in soil cultures. Besides this anatomical difference, a dif- 
ference in size was commonly observed. These two distinct types could 
