There are two species of lungworms, belonging in the genus 
Metastrongylus, in swine, these being M. elongatus and M. brevivagijua- 
tus. The eggs of these worms hatch in the lungs and the larvae are 
coughed up and swallowed, as a rule, the larvae passing out in the 
feces. The larvae of M. elongatus are 220 to 350 microns long by 10 
microns wide, clear anteriorly and granular posteriorly, and with a 
knob-like tail. 
The larvae of these lungworms must be distinguished from those 
of worms of the genus Strongyloides. Members of this genus occur 
as parasitic females which are parthenogenetic, no males being found. 
The eggs passing out in the feces usually contain embryos, which soon 
hatch under ordinary conditions, giving rise to rhabditiform larvae. 
These rhabditiform larvae may then give rise to filariform larvae, 
Fig. 27. Macracanthorhynchus hirudinaceus. Egg. Enlarged. From Travassos, 1917. 
capable of reinfesting host animals, or may develop to free-living adult 
males and females, which reproduce and give rise to rhabditiform 
larvae, which later develop to infective filariform larvae. One species 
which has been described from swine is Strongyloides suis. Another 
species which is reported from swine is the one found in ruminants, 
Str. papillosus. Ackert and Payne have recently reported the form 
from man, Str. stercoralis, from swine in the Island of Trinidad. The 
rhabditiform larva (Fig. 25) and the filariform larva (Fig. 26) of the 
human Strongyloides are figured here. 
The eggs (Fig. 27) of the thorny-headed worm of swine, 
Macracanthorhynchus hirudinaceus (Gigantorhynchus gigas) are oval, 
90 to 100 microns long by 51 to 56 microns wide, and provided with 3 
shells; the embryo is coiled up and has at the anterior end 4 large 
hooks and a number of smaller ones. 
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